Barber v. Thomas

(Slip Opinion) OCTOBER TERM, 2009 1

Syllabus

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is

being done in connection with this case, at the time the opinion is issued.

The syllabus constitutes no part of the opinion of the Court but has been

prepared by the Reporter of Decisions for the convenience of the reader.

See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.

SUPREME COURT OF THE UNITED STATES

Syllabus

BARBER ET AL. v. THOMAS, WARDEN

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR

THE NINTH CIRCUIT

No. 09–5201. Argued March 30, 2010—Decided June 7, 2010

The federal sentencing statute at issue provides that a “prisoner . . .

serving a term of imprisonment of more than 1 year . . . may receive

credit toward the service of [that] sentence . . . of up to 54 days at the

end of each year” subject to the Bureau of Prison’s (BOP) “determina

tion . . . that, during that year, the prisoner” has behaved in an ex

emplary fashion. 18 U. S. C. §3624(b)(1). Credit “for the last year or

portion of a year of the term of imprisonment [is] prorated . . . .” Ibid.

The BOP applies this statute using a methodology that awards 54

days of credit at the end of each year the prisoner serves and sets

those days to the side. When the difference between the time re

maining in the sentence and the amount of accumulated credit is less

than one year, the BOP awards a prorated amount of credit for that

final year proportional to the awards in other years.

Petitioners claim that the BOP’s calculation method is unlawful

because §3624(b)(1) requires a calculation based on the length of the

term of imprisonment imposed by the sentencing judge, not the

length of time that the prisoner actually serves. The District Court

rejected this challenge in each of petitioner’s cases, and the Ninth

Circuit affirmed.

Held: Because the BOP’s method for calculating good time credit re

flects the most natural reading of the statute, it is lawful. Pp. 5–17.

(a) The statute’s language and purpose, taken together, support the

BOP’s method. That method tracks §3624(b)’s language by providing

a prisoner a maximum credit of 54 days for each full year of impris

onment and a proportionally adjusted amount of credit for any addi

tional time served that is less than a full year. As §3624(b) directs,

the BOP awards the credit “at the end of each year” of imprisonment.

Petitioners’ approach cannot be reconciled with the statute. Because

2 BARBER v. THOMAS

Syllabus

it awards credit for the sentence imposed, regardless of how much

time is actually served, a prisoner could receive credit for a year that

he does not spend in prison. Moreover the calculation of credit for

such a year would not be made “at the end of” that year. Nor could

the BOP determine whether the prisoner had exemplary behavior

“during that year.” This language did not find its way into the stat

ute by accident. The differences between the prior provision (re

pealed in 1984)—which granted the prisoner a deduction at the out

set of his sentence, subject to forfeiture for breaking prison rules—

and the present statute—under which “credit” is “earned” “at the end

of” the year based on an evaluation of behavior “during that year”—

show an intent to move from a prospective entitlement to a retrospec

tive award. The BOP’s method also furthers the basic purpose of the

statute. Section 3624 was part of the comprehensive Sentencing Re

form Act of 1984, which sought to achieve both increased sentencing

uniformity and greater honesty by “mak[ing] all sentences basically

determinate.” Mistretta v. United States, 488 U. S. 361, 367. There

after, the sentence the judge imposed would be the one the offender

actually served, with a sole statutory exception for good time credits.

Ibid. Section 3624(b) states the reason for the exception: to provide

an incentive for prisoners to “compl[y] with institutional disciplinary

regulations.” The exception is limited and tailored to its purpose—

credit is earned at the end of the year after compliance with institu

tional rules is demonstrated and thereby rewards and reinforces a

readily identifiable period of good behavior. The BOP’s approach fur

thers §3624’s objectives by tying the award directly to good behavior

during the preceding year. In contrast, petitioners’ approach would

allow a prisoner to earn credit for both the portion of his sentence

that he served and the portion offset with earned credit, which would

loosen the statute’s connection between good behavior and the good

time award. Pp. 5–8.

(b) Arguments to the contrary are unconvincing. Context indicates

that the phrase “term of imprisonment” as used in the portion of

§3624(b) at issue here refers to prison time actually served not, as pe

titioners contend, to the sentence imposed by the judge. Petitioners’

reliance on legislative history is misplaced. A U. S. Sentencing Com

mission Supplementary Report is not helpful to them either, because

there is no indication that the Commission, in that report or in the

Guidelines themselves, considered or referred to the particular ques

tion whether to base good time credit on time served or the sentence

imposed. Nor, in light of the statute’s text, structure, history, and

purpose, is this a case in which there is a “grievous ambiguity or un

certainty in the statute,” Muscarello v. United States, 524 U. S. 125,

139, permitting application of the rule of lenity. Because the BOP’s

Cite as: 560 U. S. ____ (2010) 3

Syllabus

calculation system applies the statute as its language is most natu

rally read, and in accordance with the statute’s basic purpose, this

Court need not determine the extent to which Congress has granted

the BOP authority to interpret the statute more broadly, or differ

ently than it has done here. Cf. Chevron U. S. A. Inc. v. Natural Re

sources Defense Council, Inc., 467 U. S. 837, 844–845. And because

the BOP’s approach reflects the statute’s most natural reading and is

the most consistent with its purpose, it is also preferable to the dis

sent’s alternative interpretation. Pp. 8–17.

Affirmed.

BREYER, J., delivered the opinion of the Court, in which ROBERTS,

C. J., and SCALIA, THOMAS, ALITO, and SOTOMAYOR, JJ., joined. KEN-

NEDY, J., filed a dissenting opinion in which STEVENS and GINSBURG,

JJ., joined.

Cite as: 560 U. S. ____ (2010) 1

Opinion of the Court

NOTICE: This opinion is subject to formal revision before publication in the

preliminary print of the United States Reports. Readers are requested to

notify the Reporter of Decisions, Supreme Court of the United States, Wash

ington, D. C. 20543, of any typographical or other formal errors, in order

that corrections may be made before the preliminary print goes to press.

SUPREME COURT OF THE UNITED STATES

_________________

No. 09–5201

_________________

MICHAEL GARY BARBER, ET AL., PETITIONERS v.

J. E. THOMAS, WARDEN

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF

APPEALS FOR THE NINTH CIRCUIT

[June 7, 2010]

JUSTICE BREYER delivered the opinion of the Court.

Federal sentencing law permits federal prison authori

ties to award prisoners credit against prison time as a

reward for good behavior. 18 U. S. C. §3624(b). Petition

ers, two federal prisoners, challenge the method that the

Federal Bureau of Prisons uses for calculating this “good

time credit.” We conclude that the Bureau’s method re

flects the most natural reading of the statute, and we

reject petitioners’ legal challenge.

I

A

A federal sentencing statute provides:

“[A] prisoner who is serving a term of imprisonment of

more than 1 year . . . may receive credit toward the

service of the prisoner’s sentence, beyond the time

served, of up to 54 days at the end of each year of the

prisoner’s term of imprisonment, beginning at the end

of the first year of the term . . . . [C]redit for the last

year or portion of a year of the term of imprisonment

shall be prorated and credited within the last six

weeks of the sentence.” §3624(b)(1).

2 BARBER v. THOMAS

Opinion of the Court

The Bureau of Prisons (BOP) applies this statute using a

methodology that petitioners in this case challenge as

unlawful. In order to explain the BOP method, we shall

use a simplified example that captures its essential ele

ments. The unsimplified calculations described by the

BOP in its policy statement, see App. 96–100, will reach

approximately the same results as, and are essentially the

mathematical equivalent of, the simplified system we

describe (there may be other ways to describe the calcula

tion as well). To the extent that there are any differences

between the methodology employed by the BOP and that

reflected in our example, they are of no consequence to the

resolution of petitioners’ challenge and are therefore not

before us. Similarly, although petitioners committed their

crimes before the current version of §3624 was enacted

and are therefore subject to a previous version that dif

fered slightly in certain details, see 18 U. S. C. §3624

(1988 ed.), the differences between the two versions are

immaterial to the questions presented by this case. The

parties refer to the current version as the relevant provi

sion of law, see Brief for Petitioners 2–3; Brief for Respon

dent 8, n. 2, and we shall do the same.

In our example we shall imagine a prisoner who has

received a sentence of 10 years’ imprisonment. We shall

assume that his behavior throughout his confinement is

exemplary and that prison authorities will consequently

consider him to merit the maximum good time credit that

the statute will allow. And we shall ignore leap years.

Thus, at the end of the first year (Year 1) that prisoner

would earn the statute’s maximum credit of 54 days. The

relevant official (whom we shall call the “good time calcu

lator”) would note that fact and, in effect, preliminarily

put the 54 days to the side. At the end of Year 2 the pris

oner would earn an additional 54 days of good time credit.

The good time calculator would add this 54 days to the

first 54 days, note the provisional total of 108 days, and

Cite as: 560 U. S. ____ (2010) 3

Opinion of the Court

again put the 108 days’ credit to the side. By the end of

Year 8, the prisoner would have earned a total of 432 days

of good time credit (8 years times 54 days). At that time,

the good time calculator would note that the difference

between the time remaining in the sentence (2 years, or

730 days) and the amount of accumulated good time credit

(432 days) is less than 1 year (730 minus 432 equals 298

days, which is less than 365). The 432 days of good time

credit that the prisoner has earned by the end of Year 8

are sufficient to wipe out all of the last year of the 10-year

prison term and to shorten the prisoner’s 9th year of im

prisonment by 67 days.

Year 9 of the sentence will consequently become the

prisoner’s last year of imprisonment. Further, because the

prisoner has already earned 67 days of credit against that

year (432 days already earned minus 365 days applied to

Year 10 leaves 67 days to apply to Year 9), the prisoner

will have no more than 298 days left to serve in Year 9.

Now the good time calculator will have to work out just

how much good time the prisoner can earn, and credit

against, these remaining 298 days.

As we said, the statute provides that “good time” for this

“last year or portion” thereof shall be “prorated.” Thus,

the good time calculator must divide the 298 days into two

parts: (1) days that the prisoner will have to serve in

prison, and (2) credit for good behavior the prisoner will

earn during the days served in Year 9. In other words, the

number of days to be served in Year 9 plus the number of

good time credit days earned will be equal to the number

of days left in the sentence, namely, 298. And to keep the

award of credit in the last year proportional to awards in

other years, the ratio of these two parts of Year 9 (i.e., the

number of good time days divided by the number of days

served) must be 54/365, the same ratio that the BOP

applies to full years served. We can use some elementary

algebra, described in the Appendix, infra, to work out the

4 BARBER v. THOMAS

Opinion of the Court

rest. The result is that if the prisoner serves 260 days, he

can earn an additional 38 days of credit for good behavior.

That is to say, of the 298 days remaining in his sentence,

the prisoner will have to serve 260 days in confinement,

after which point, his sentence will be fully accounted for

(given the additional 38 days’ credit earned), and he will

be released. In sum, a prisoner subject to a 10-year

(3,650-day) sentence who earns the maximum number of

days the statute permits will serve 3,180 days in confine

ment and receive 470 days of “good time” credit, about

15% of the prison time actually served.

B

In this case petitioners claim that the BOP’s calculation

method is unlawful. They say that §3624(b)(1) (2006 ed.)

requires a straightforward calculation based upon the

length of the term of imprisonment that the sentencing

judge imposes, not the length of time that the prisoner

actually serves. Thus, if a sentencing judge imposes a

prison term of 10 years (as in our example), then, in peti

tioners’ view, the statute permits a maximum good time

award of 540 days (10 years times 54 days), not the 470

days that the method described above would allow. And if

the judge imposes a prison term of 10 years and 6 months,

then the statute permits 567 days (540 days for the 10

years plus 27 days for the extra 6 months), not the 494

days that the method above would allow. According to

petitioners, the BOP’s method causes model prisoners to

lose seven days of good time credit per year of imprison

ment, and because their sentences are fairly long (one,

Michael Barber, was sentenced to 26 years and 8 months;

the other, Tahir Jihad-Black, was sentenced to 21 years

and 10 months), the difference in their cases amounts to

several months of additional prison time.

The District Court in each of these cases rejected the

prisoner’s challenge. Civ. No. 08–226 MO (D Ore., Oct. 27,

Cite as: 560 U. S. ____ (2010) 5

Opinion of the Court

2008), App. 13; Jihad-Black v. Thomas, Civ. No. 08–227

MO (D Ore., Oct. 27, 2008), App. 25. And in each instance

the Court of Appeals affirmed the District Court. Tablada

v. Thomas, No. 07–35538 (CA9, Apr. 10, 2009), App. 11;

see also Tablada v. Thomas, 533 F. 3d 800 (CA9 2008).

Because the BOP’s administration of good time credits

affects the interests of a large number of federal prisoners,

we granted the consolidated petition for certiorari to con

sider petitioners’ challenge.

II

Having now considered petitioners’ arguments, we

conclude that that we must reject their legal challenge.

The statute’s language and its purpose, taken together,

convince us that the BOP’s calculation method is lawful.

For one thing, that method tracks the language of

§3624(b). That provision says that a prisoner (serving a

sentence of imprisonment of more than a year and less

than life) “may receive credit . . . of up to 54 days at the

end of each year” subject to the “determination by the

Bureau of Prisons that, during that year, the prisoner” has

behaved in an exemplary fashion. Ibid. (emphasis added).

And it says that credit for the “last year or portion of a

year . . . shall be prorated and credited within the last six

weeks of the sentence.” Ibid. As the example in Part I

makes clear, the BOP’s interpretation provides a prisoner

entitled to a maximum annual credit with 54 days of good

time credit for each full year of imprisonment that he

serves and a proportionally adjusted amount of credit for

any additional time served that is less than a full year.

And, as §3624(b) directs, the BOP awards the credit at the

end of each year of imprisonment (except, of course, for

Year 9, which is subject to the statute’s special instruction

requiring proration and crediting during the last six weeks

of the sentence).

We are unable similarly to reconcile petitioners’ ap

6 BARBER v. THOMAS

Opinion of the Court

proach with the statute. Their system awards credit for

the sentence imposed, regardless of how much time is

actually served. Thus, a prisoner under petitioners’ sys

tem could receive 54 days of credit for Year 10 despite the

fact that he would be released after less than 81⁄2 years in

prison. The good time calculation for Year 10 would not be

made “at the end of” Year 10 (nor within the last six weeks

of a sentence ending during that year). Neither could the

BOP determine whether the prisoner had behaved in

exemplary fashion “during that year.” 18 U. S. C. §3624(b)

(emphasis added); see also White v. Scibana, 390 F. 3d

997, 1001 (CA7 2004) (“The Bureau cannot evaluate a

prisoner’s behavior and award credit for good conduct if

the prisoner is not still in prison”); cf. McGinnis v. Royster,

410 U. S. 263, 273 (1973) (“Where there is no evaluation

by state officials and little or no rehabilitative participa

tion for anyone to evaluate, there is a rational justification

for declining to give good-time credit”).

We cannot say that this language (“at the end of,” “dur

ing that year”) found its way into the statute by accident.

Under the previous good time provision, a prisoner was

“entitled to a deduction from the term of his sentence

beginning with the day on which the sentence commences

to run.” 18 U. S. C. §4161 (1982 ed.) (repealed 1984). This

deduction, granted at the outset of a prisoner’s sentence,

was then made subject to forfeiture if the prisoner “com

mit[ted] any offense or violate[d] the rules of the institu

tion.” §4165 (repealed 1984). The present statute, §3624

(2006 ed.), in contrast, creates a system under which

“credit” is “earned” “at the end of” the year based on an

evaluation of behavior “during that year.” We agree with

the Government that “[t]he textual differences between

the two statutes reveal a purpose to move from a system of

prospective entitlement to a system of retrospective

award.” Brief for Respondent 33; see also White, supra, at

1002, n. 3.

Cite as: 560 U. S. ____ (2010) 7

Opinion of the Court

For another thing, the BOP’s method better furthers the

statute’s basic purpose. The “good time” provision in

§3624 is part of the Sentencing Reform Act of 1984, 98

Stat. 1987, 18 U. S. C. §3551 et seq., 28 U. S. C. §§991–

998, a comprehensive law that reformed federal sentenc

ing practice and directed the newly created United States

Sentencing Commission “to devise guidelines to be used

for sentencing” in district courts, Mistretta v. United

States, 488 U. S. 361, 367 (1989). Under the previous

regime, the United States Parole Commission, “as a gen

eral rule, [could] conditionally release a prisoner any time

after he serve[d] one-third of the judicially fixed term.”

United States v. Grayson, 438 U. S. 41, 47 (1978). If, for

example, a judge imposed a prison term of 15 years, the

Parole Commission might have released the prisoner after

only 5 years. And it routinely did so. See United States

Sentencing Commission, Guidelines Manual §1A3, p. s., p.

1.2 (Oct. 1987) (USSG) (“[D]efendants often serv[ed] only

about one-third of the sentence handed down by the

court”). The result was “confusion and implicit deception.”

Ibid. With the Sentencing Reform Act, Congress sought to

achieve both increased sentencing uniformity and greater

honesty by “mak[ing] all sentences basically determinate,”

Mistretta, supra, at 367. See USSG §1A3, p. s., at 1.2

(statutory objectives included “honesty in sentencing,”

“uniformity,” and “proportionality” (emphasis deleted)).

Thereafter, the sentence the judge imposed would be the

sentence the offender actually served, with a sole statutory

exception for good time credits. Mistretta, supra, at 367 (a

“prisoner is to be released at the completion of his sen

tence reduced only by any credit earned by good behavior

while in custody” (citing §3624(b)). The reason for this

exception is provided in §3624(b) itself: to provide an

incentive for prisoners to “compl[y] with institutional

disciplinary regulations.” The good time exception is

limited (to 54 days per year) and tailored to its purpose—

8 BARBER v. THOMAS

Opinion of the Court

credit is earned at the end of the year after compliance

with institutional rules is demonstrated and thereby

rewards and reinforces a readily identifiable period of good

behavior.

The BOP’s approach furthers the objective of §3624. It

ties the award of good time credits directly to good behav

ior during the preceding year of imprisonment. By con

trast, petitioners’ approach, insofar is it would award up to

54 days per year of time sentenced as opposed to time

served, allows a prisoner to earn credit for both the portion

of his sentence that he serves and the portion of his sen

tence that he offsets with earned good time credit. In

other words, petitioners argue that the BOP should award

good time credit not only for the days a prisoner spends in

prison and behaves appropriately, but also for days that

he will not spend in prison at all, such as Year 10 in our

example. By doing so, it loosens the statute’s connection

between good behavior and the award of good time and

transforms the nature of the exception to the basic sen

tence-imposed-is-sentence-served rule. And to that extent,

it is inconsistent with the statute’s basic purpose.

III

A

We are not convinced by petitioners’ several arguments

against the BOP’s methodology. First, petitioners point to

the statement in §3624(b) that a prisoner “may receive

credit . . . at the end of each year of the prisoner’s term of

imprisonment.” (Emphasis added.) The words “term of

imprisonment,” they say, must refer to the years of the

term that the sentencing judge imposed (10 years in our

example), not the (less-than-10) years of the term that the

prisoner actually served once good time credits were taken

into account. After all, the very first phrase of that provi

sion makes eligible for good time credits “a prisoner who is

serving a term of imprisonment of more than 1 year other

Cite as: 560 U. S. ____ (2010) 9

Opinion of the Court

than a term of imprisonment for the duration of the pris

oner’s life.” Ibid. (emphasis added; footnote omitted). The

words “term of imprisonment” in this phrase almost cer

tainly refer to the sentence imposed, not to the time actu

ally served (otherwise prisoners sentenced to a year and a

day would become ineligible for credit as soon as they

earned it). And, as petitioners emphasize, we have recog

nized a “presumption that a given term is used to mean

the same thing throughout a statute,” Brown v. Gardner,

513 U. S. 115, 118 (1994).

The problem for petitioners, however, is that this pre

sumption is not absolute. It yields readily to indications

that the same phrase used in different parts of the same

statute means different things, particularly where the

phrase is one that speakers can easily use in different

ways without risk of confusion. Atlantic Cleaners & Dyers,

Inc. v. United States, 286 U. S. 427, 433 (1932); General

Dynamics Land Systems, Inc. v. Cline, 540 U. S. 581, 595–

596 (2004). See, e.g., id., at 596–597 (“age” has different

meanings in the Age Discrimination in Employment Act of

1967); United States v. Cleveland Indians Baseball Co.,

532 U. S. 200, 213 (2001) (same for “ ‘wages paid’ ” in the

Internal Revenue Code); Robinson v. Shell Oil Co., 519

U. S. 337, 343–344 (1997) (same for “employee” in Title

VII of the Civil Rights Act of 1964).

The phrase “term of imprisonment” is just such a

phrase. It can refer to the sentence that the judge im

poses, see, e.g., §3624(a) (“A prisoner shall be released” at

the end of “the prisoner’s term of imprisonment, less any

time credited” for good behavior), but it also can refer to

the time that the prisoner actually serves. Thus, §3624(d)

of the statute before us requires BOP to “furnish [a] pris

oner with . . . suitable clothing[,] . . . money, . . . and . . .

transportation” “[u]pon the release of [the] prisoner on the

expiration of the prisoner’s term of imprisonment.” (Em

phasis added.) The statute here means to assure that the

10 BARBER v. THOMAS

Opinion of the Court

prisoner is provided with these necessities at the time of

his actual release from prison (sometime during Year 9 in

our example), not at the end of the term that the judge

imposed (which would be over a year later). Since the

statute uses the same phrase “term of imprisonment” in

two different ways, the presumption cannot help petition

ers here. And, for the reasons we have given, see Part II,

supra, context here indicates that the particular instance

of the phrase “term of imprisonment” at issue refers to

prison time actually served rather than the sentence

imposed by the judge.

Second, petitioners seek to draw support from the stat

ute’s legislative history. But those who consider legisla

tive history significant cannot find that history helpful to

petitioners here. Petitioners point, for example, to a

statement in the Senate Report accompanying the Sen

tencing Reform Act, which says that the “method of calcu

lation” of good time “will be considerably less complicated

than under current law in many respects,” and that “credit

toward early release is earned at a steady and easily

determined rate that will have an obvious impact on the

prisoner’s release date.” S. Rep. No. 98–225, p. 146–147

(1983); see Brief for Petitioners 31–32. But these state

ments are consistent with the BOP’s interpretation of the

statute. Its method, as we understand it, is not particu

larly difficult to apply and it is certainly less complex than

prior law, which provided for the accumulation of two

different kinds of good time credit (general and industrial),

calculated in different manners (prospectively and retro

spectively), and awarded at different rates, depending on

the length of sentence imposed on the prisoner (5 to 10

days per month for general) or the year of employment (3

or 5 days per month for industrial). See 18 U. S. C.

§§4161, 4162 (1982 ed.).

Petitioners also point to various statements contained in

the Act’s Conference Report and made by individual legis

Cite as: 560 U. S. ____ (2010) 11

Opinion of the Court

lators that describe good time credit as providing sentence

reductions of 15%. See Brief for Petitioners 34–36 (citing,

e.g., H. R. Conf. Rep. No. 98–1159, p. 415 (1984); 131

Cong. Rec. 488 (1985) (remarks of Rep. Hamilton)). But

there is nothing in the context of these statements to

suggest that they amounted to anything other than rough

approximations or that they were made with the present

controversy in mind. See, e.g., H. R. Conf. Rep. No. 98–

1159, at 415 (noting simply that an increase in the amount

of maximum annual credit from 36 days to 54 days “in

creases ‘good time’ that accrues from 10 percent to 15

percent”); 131 Cong. Rec. 488 (1985) (statement of Rep.

Hamilton) (“Under [pre-Sentencing Reform Act] law, about

80% of all criminals are paroled after serving one third of

their time. Now sentences will be reduced only 15% for

good behavior”). And whatever interpretive force one

attaches to legislative history, the Court normally gives

little weight to statements, such as those of the individual

legislators, made after the bill in question has become law.

See, e.g., Heintz v. Jenkins, 514 U. S. 291, 298 (1995).

Third, petitioners rely on a statement in the United

States Sentencing Commission’s Supplementary Report on

the Initial Sentencing Guidelines and Policy Statements

issued in 1987 (hereinafter Supplementary Report). In

that Report, the Commission summarized its analysis of

recent pre-Guidelines sentencing practice, which it had

used to help draft the Guidelines. The results of the

analysis were presented in a table that permits compari

son of the likely prison-time consequences of the new

Guidelines with prison time actually served under pre-

Guidelines practice (specifically, by identifying the Guide

lines “offense level that is closest to the average time . . .

served by first-time offenders” convicted of a particular

crime, Supplementary Report 23). Because the Guidelines

“refer to sentences prior to the awarding of good time” (i.e.,

because a Guidelines sentence of, say, 30 months’ impris

12 BARBER v. THOMAS

Opinion of the Court

onment does not necessarily mean that the offender will

serve the entire 30 months in prison), the Commission

adjusted the average time served “by dividing by 0.85 good

time when the term exceeded 12 months.” Ibid. This

adjustment, the Commission explained, “made sentences

in the [t]able comparable with those in the guidelines.”

Ibid.

Pointing to this adjustment and a reference in later

editions of the Guidelines to a potential credit of “ap

proximately fifteen percent for good behavior,” see, e.g.,

USSG §1A3, p. s., at 3 (Nov. 2009), petitioners maintain

that the Commission set its Guideline ranges with the

expectation that well-behaved prisoners would receive

good time credit of up to 15% of the sentence imposed, not

15% of the time actually served. They add that, in setting

the Guidelines ranges in this way, the Commission exer

cised congressionally delegated power to interpret the

Sentencing Reform Act, see Mistretta, 488 U. S., at 371–

379 (approving Congress’ delegation of the power to prom

ulgate sentencing guidelines), and that as long as that

interpretation is reasonable, courts must defer to it. See

Chevron U. S. A. Inc. v. Natural Resources Defense Coun

cil, Inc., 467 U. S. 837, 843–844 (1984).

Again, however, we can find no indication that the

Commission, in writing its Supplementary Report or in

the Guidelines themselves, considered or referred to the

particular question here before us, that is whether good

time credit is to be based on time served or the sentence

imposed. The Guidelines Manual itself, a more authorita

tive account of the Commission’s interpretive views than

the Supplementary Report, says nothing directly on that

subject. Moreover, with respect to comparisons between

Guidelines sentences and pre-Guidelines practice, the

original 1987 Manual cautioned that the Guidelines did

not “simply cop[y] estimates of existing practice as re

vealed by the data,” but rather “departed from the data at

Cite as: 560 U. S. ____ (2010) 13

Opinion of the Court

different points for various important reasons.” USSG

§1A3, p. s., at 1.4; see also id., §1A4(g), p. s., at 1.11

(while “Guideline sentences in many instances will ap

proximate existing [i.e., pre-Guidelines] practice,” the

Commission did “not conside[r] itself bound by existing

sentencing practice” (emphasis added)). Because the

Commission has expressed no view on the question before

us, we need not decide whether it would be entitled to

deference had it done so. If it turns out that the calcula

tion of good time credit based on prison time served rather

than the sentence imposed produces results that are more

severe than the Commission finds appropriate, the Com

mission remains free to adjust sentencing levels accord

ingly. See id., §1A2, at 1.2 (acknowledging that “the

guideline-writing process is evolutionary” and that the

Commission functions “as a permanent agency to monitor

sentencing practices in the federal courts throughout the

nation”).

Fourth, petitioners ask us to invoke the rule of lenity

and construe §3624 (2006 ed.) in their favor, that is, in a

way that will maximize the amount of available good time

credit. We may assume for present purposes that §3624(b)

can be construed as imposing a criminal penalty. See

Bifulco v. United States, 447 U. S. 381, 387 (1980) (rule of

lenity applies to “interpretations of . . . the penalties”

imposed by “criminal prohibitions”); but see Sash v. Zenk,

428 F. 3d 132, 134 (CA2 2005) (Sotomayor, J.) (holding

that §3624(b) is not a criminal statute for the purposes of

the rule of lenity). Even so, the rule of lenity only applies

if, after considering text, structure, history, and purpose,

there remains a “grievous ambiguity or uncertainty in the

statute,” Muscarello v. United States, 524 U. S. 125, 139

(1998) (internal quotation marks omitted), such that the

Court must simply “ ‘guess as to what Congress intended.’ ”

Bifulco, supra, at 387 (quoting Ladner v. United States,

358 U. S. 169, 178 (1958)). See United States v. Hayes,

14 BARBER v. THOMAS

Opinion of the Court

555 U. S. ___, ___ (2009) (slip op., at 13); United States v.

R. L. C., 503 U. S. 291, 305–306 (1992) (plurality opinion).

Having so considered the statute, we do not believe that

there remains a “grievous ambiguity or uncertainty” in the

statutory provision before us. Nor need we now simply

“guess” what the statute means.

Finally, we note that petitioners urge us not to defer to

the BOP’s implementation of §3624(b). In our view, the

BOP’s calculation system applies that statute as its lan

guage is most naturally read, and in accordance with what

that language makes clear is its basic purpose. No one

doubts that the BOP has the legal power to implement the

statute in accordance with its language and purposes;

hence we need not determine the extent to which Congress

has granted the BOP authority to interpret the statute

more broadly, or differently than it has done here. Cf.

Chevron, supra, at 844–845.

B

Acknowledging that petitioners’ arguments cannot carry

the day, the dissent has proposed a “third possibility,”

post, at 2 (opinion of KENNEDY, J.), not raised by either

party nor, to our knowledge, used elsewhere in the Crimi

nal Code. The dissent reads the statutory phrase “term of

imprisonment” to refer to “the administrative period along

which progress toward eventual freedom is marked.” Post,

at 3. It derives from this reading the following method of

calculation as applied to our 10-year example. First, “[t]he

sentence is divided into 10 365-day segments.” Ibid. At

the end of the first segment, a prisoner may receive up to

54 days of credit for good behavior. These credits immedi

ately “go toward completion of the next year” so that the

prisoner need only serve “another 311 days behind bars

before the second year of his term of imprisonment is at an

end.” Ibid. This process repeats itself until the “10th

segment,” in which a prisoner receives an unspecified

Cite as: 560 U. S. ____ (2010) 15

Opinion of the Court

“credit in a prorated amount.” Ibid. In the end, the pris

oner will have served 10 “administrative segments,” ibid.,

collectively comprising 3,117 days in prison and 533 days

of credit.

The dissent claims “[r]eading ‘term of imprisonment’

this way is consistent with all parts of the statute.” Post,

at 4. We see at least four problems. First, the opening

sentence of §3624(a) instructs that “[a] prisoner shall be

released” upon “the expiration of the prisoner’s term of

imprisonment, less any time credited” for good behavior.

But if a prisoner’s “term of imprisonment” is the “period

that a prisoner must complete in order to earn his free

dom,” post, at 4, and it is “accounted for through a combi

nation of prison time and credits,” post, at 3, then a pris

oner should be released exactly at the end of his term of

imprisonment (without any further adjustment). Because

the dissent’s approach would require us to read words out

of the statute, or give prisoners double credit, its definition

cannot be used here.

Second, §3624(b)(1) tells us that a prisoner receives

credit “at the end of each year” based on behavior “during

that year.” Under the dissent’s approach, however, a

prisoner may receive credit at the end of each “administra

tive segmen[t]” presumably based on his behavior during

that segment. And because an “administrative segmen[t]”

is made up of some “combination of service and credits,”

post, at 4, each one lasts less than a calendar year. We do

not see how a system in which “a prisoner may complete a

particular year of his term in less than 365 calendar days,”

ibid., and receive full good time credit for doing so, can

possibly represent the most natural reading of this statu

tory language. Nor do we know, because the BOP has not

had an opportunity to tell us, whether a system in which a

“year” lasts anywhere from 311 to 365 calendar days (and

in which the “years” of a single prisoner’s sentence may all

be of different lengths), is easily administrable. (We doubt

16 BARBER v. THOMAS

Opinion of the Court

that this system will be more comprehensible to prisoners

than one, like the BOP’s, that provides credit for actual

years.)

Third, under the dissent’s approach, credit is earned at

different rates during a single sentence. For the first

“administrative segmen[t]” in its 10-year example, the

prisoner serves 365 days and earns 54 days of credit. The

ratio of credit earned to days served is .148. For the sec

ond “administrative segmen[t],” the prisoner serves 311

days and earns 54 days of credit. This time, the ratio of

credit earned to days served is .174. (For the last “admin

istrative segmen[t],” the dissent tells us the prisoner will

receive “credit in a prorated amount,” but it does not tell

us which ratio should be used for the proration. Post, at

3.) The use of different rates finds no support in the stat

ute. The dissent objects that the statute “prescribes no

particular rate,” post, at 7, but in fact it does—54 days of

credit per year of good behavior—and it further requires

that credit for the last year be “prorated” using the same

proportion. Moreover, the dissent’s application of different

rates leads to odd results. For example, a model prisoner

sentenced on two separate 5-year terms (with a break in

between) will serve a different number of days from one

sentenced to a single 10-year term. How can this be if

both prisoners are earning 54 days of credit for each of

their 10 years in prison?

Fourth, §3624(b)(2) provides that good time credit “shall

vest on the date the prisoner is released from custody.”

(This provision does not apply to prisoners, like petition

ers, who committed their offenses before it was amended

in 1996, but the dissent plainly intends for its approach to

apply more broadly. See post, at 9 (noting the effect on

“almost 200,000 federal prisoners”).) Yet under the dis

sent’s approach, credit appears to vest immediately. See

post, at 3 (Days of credit for the first year “go toward

completion of the next year” so that the prisoner “would

Cite as: 560 U. S. ____ (2010) 17

Opinion of the Court

need another 311 days behind bars before the second year

of his term of imprisonment is at an end”). And if it does

not, then the situation quickly becomes complicated.

What happens if, say, on the last day of the 10th “adminis

trative segmen[t]” (somewhere in the 8th calendar year), a

prisoner badly misbehaves and prison officials punish him

by taking away all of his previously earned credit? Cf. 28

CFR §541.13 (2009) (prescribing sanctions for prohibited

acts). Does the BOP retroactively adjust the duration of

all of his administrative segments to 365 days so that the

prisoner now finds himself in the middle of the 8th “ad

ministrative segmen[t]”? (Again we do not know if the

BOP would find such a system administrable, and we

doubt that this system would be more comprehensible to a

prisoner.) If so, does the prisoner have a second opportu

nity to earn credit for good behavior for the 9th “adminis

trative segmen[t]” that he had previously completed but

now must account for again? Cf. §3624(b)(1) (“Credit that

has not been earned may not later be granted”). Or, hav

ing previously awarded (and taken away) credit for that

segment, are prison authorities left without any incentive

to offer for good behavior?

Finally, the dissent, like petitioners, invokes the rule of

lenity to support its interpretation. But, the best efforts of

the dissent notwithstanding, we still see no “grievous

ambiguity or uncertainty” that would trigger the rule’s

application. We remain convinced that the BOP’s ap

proach reflects the most natural reading of the statutory

language and the most consistent with its purpose. What

ever the merits of the dissent’s policy arguments, the

statute does not require the BOP to accept them.

For all of these reasons, we conclude that the BOP’s

methodology is lawful. The Ninth Circuit’s judgment is

Affirmed.

18 BARBER v. THOMAS

Opinion of the Court

Appendix to opinion of the Court

APPENDIX

A fuller example of the BOP’s method for calculat

ing “credit for the last year or portion of a year of

the term of imprisonment”

The defendant is sentenced to 10 years’ imprisonment.

As a prisoner he exhibits exemplary behavior and is

awarded the maximum credit of 54 days at the end of each

year served in prison. At the end of Year 8, the prisoner

has 2 years remaining in his sentence and has accumu

lated 432 days of good time credit. Because the difference

between the time remaining in his sentence and the

amount of accumulated credit (i.e., 730 - 432) is less than a

year (298 days), Year 9 is the last year he will spend in

prison. (Year 10 has been completely offset by 365 of the

432 days of accumulated credit.) Further, Year 9 will be a

partial year of 298 days (the other 67 days of the year

being offset by the remainder of the accumulated credit).

Here is where the elementary algebra comes in. We

know that x, the good time, plus y, the remaining time

served, must add up to 298. This gives us our first equa

tion: x + y = 298.

We also know that the ratio of good time earned in the

portion of the final year to the amount of time served in

that year must equal the ratio of a full year’s good time

credit to the amount of time served in a full year. The

latter ratio is 54/365 or .148. Thus, we know that

x/y = .148, or to put it another way, x = .148y. Because we

know the value of x in terms of y, we can make a substitu

tion in our first equation to get .148y + y = 298. We then

add the two y terms together (1.148y = 298), and we solve

for y, which gives us y = 260. Now we can plug that value

into our first equation to solve for x (the good time credit).

If we subtract 260 from 298, we find that x = 38.

The offender will have to serve 260 days in prison in

Year 9, and he will receive 38 days additional good time

Cite as: 560 U. S. ____ (2010) 19

Opinion of the Court

Appendix to opinion of the Court

credit for that time served. The prisoner’s total good time

is 470 days (432 + 38 = 470). His total time served is 3180

days.

As a final matter, while we have described the foregoing

as the method to calculate credit for the portion of the last

year to more transparently track the relevant statutory

language, we note that the mathematical formula can be

used to calculate the amount of maximum available credit

for an entire sentence. Using the equations supplied

above, if we divide the total number of days in a sentence

by 1.148, we get the minimum number of days that a

defendant must serve in that sentence. If we then sub

tract the number of days served from the total number of

days in the sentence, we arrive at the maximum number

of good time credit days the prisoner can earn. The stat

ute, however, awards them on a yearly basis (but for the

“last year or portion” thereof).

Cite as: 560 U. S. ____ (2010) 1

KENNEDY, J., dissenting

SUPREME COURT OF THE UNITED STATES

_________________

No. 09–5201

_________________

MICHAEL GARY BARBER, ET AL., PETITIONERS v.

J. E. THOMAS, WARDEN

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF

APPEALS FOR THE NINTH CIRCUIT

[June 7, 2010]

JUSTICE KENNEDY, with whom JUSTICE STEVENS and

JUSTICE GINSBURG join, dissenting.

The Court has interpreted a federal sentencing statute

in a manner that disadvantages almost 200,000 federal

prisoners. See Pet. for Cert. 11, and n. 2. It adopts this

reading despite the existence of an alternative interpreta

tion that is more consistent with the statute’s text. Absent

a clear congressional directive, the statute ought not to be

read as the Court reads it. For the Court’s interpreta

tion—an interpretation that in my submission is quite

incorrect—imposes tens of thousands of years of additional

prison time on federal prisoners according to a mathe

matical formula they will be unable to understand. And if

the only way to call attention to the human implications of

this case is to speak in terms of economics, then it should

be noted that the Court’s interpretation comes at a cost to

the taxpayers of untold millions of dollars. See id., at 11.

The interpretation the Court adopts, moreover, will be

devastating to the prisoners who have behaved the best

and will undermine the purpose of the statute. These

considerations, and those stated below, require this re

spectful dissent.

I

The federal sentencing statute at issue here provides:

2 BARBER v. THOMAS

KENNEDY, J., dissenting

“[A] prisoner who is serving a term of imprisonment of

more than 1 year[,] other than a term of imprisonment

for the duration of the prisoner’s life, may receive

credit toward the service of the prisoner’s sentence,

beyond the time served, of up to 54 days at the end of

each year of the prisoner’s term of imprisonment, be

ginning at the end of the first year of the term, subject

to determination by the Bureau of Prisons that, dur

ing that year, the prisoner has displayed exemplary

compliance with institutional disciplinary regula

tions. . . . [C]redit for the last year or portion of a year

of the term of imprisonment shall be prorated and

credited within the last six weeks of the sentence.” 18

U. S. C. §3624(b)(1) (emphasis added).

According to the Court, the phrase “term of imprisonment”

must mean “time actually served” the third time that it

appears in this particular subsection. But the Court gives

the phrase a different interpretation the first two times it

is used in the very same sentence. This in itself indicates

that something is quite wrong here.

Petitioners invite the Court to read “term of imprison

ment” to mean “the sentence imposed.” This, too, seems

unworkable. And it can be acknowledged that the Court’s

rejection of this interpretation is correct.

The choice, however, is not just between the Court’s

reading and that offered by petitioners. There is a third

possibility, one more consistent with the statute than

either of these two alternatives.

A fair reading of the statute, and a necessary reading to

accomplish its purpose best, is to interpret the phrase

“term of imprisonment” to refer to the span of time that a

prisoner must account for in order to obtain release. The

length of the term is set at the outset by the criminal

sentence imposed. The prisoner earns release when that

term has been fully completed. Most of the term will be

Cite as: 560 U. S. ____ (2010) 3

KENNEDY, J., dissenting

satisfied through time spent behind bars. Assuming the

prisoner is well behaved, however, he may earn good time

credits along the way; and those credits may substitute for

actual prison time. Each year of the term comprises a full

365 days, which must be accounted for through a combina

tion of prison time and credits. Thus conceived, a pris

oner’s “term” is the administrative period along which

progress toward eventual freedom is marked.

Consider the Court’s example of a prisoner subject to a

ten-year sentence. See ante, at 2–4. The sentence is

divided into ten 365-day segments. Each segment consti

tutes a year of the term. The prisoner will spend the first

365 days behind bars. In the statute’s words, he has

reached “the end of the first year of the term.” Now is the

time for credit to be awarded, and he may receive up to 54

days if sufficiently well behaved. Because he has already

completed a full year of his term, those credits go toward

completion of the next year. If, based on good behavior, he

has earned the maximum of 54 days, he would need an

other 311 days behind bars before the second year of his

term of imprisonment is at an end (because 54 + 311 =

365). If he has earned fewer than 54 days, a longer incar

ceration will be required to reach 365. Regardless, once

the prisoner reaches the end of the second year of his

term, he will again be eligible to receive good time credits.

This process repeats itself for the third year of the term,

and so on. In the final year of his term (in this example,

the tenth segment into which his term has been divided),

the prisoner will receive credit in a prorated amount, to be

awarded “within the last six weeks of the sentence.” This

ensures that the prisoner does not reach the end of year

ten, only to find that he has just earned 54 days of credit

he no longer needs.

The controlling rule is that each year of the prisoner’s

term—each of the ten administrative segments—

comprises 365 days that must be completed through a

4 BARBER v. THOMAS

KENNEDY, J., dissenting

combination of service and credits. By combining actual

prison time with the credits he has earned, a prisoner may

complete a particular year of his term in less than 365

calendar days. As a result, credits may enable a well

behaved prisoner to complete his ten-year sentence before

ten calendar years have elapsed. For a ten-year (3,650

day) sentence, a prisoner will serve 3,117 days behind bars

if he earns a maximum of approximately 533 credits. This

is 63 more days of credit than under the Court’s reading—

more than 6 additional credit days for every year of the

sentence imposed.

Reading “term of imprisonment” this way is consistent

with all parts of the statute. The prisoner receives his

credit “at the end of each year of [his] term of imprison

ment,” a process that “begin[s] at the end of the first year

of the term.” Credit is only awarded if the prisoner has

proven well behaved “during that year.” This interpreta

tion fulfills the “objective of §3624”—rewarding a prisoner

for exemplary conduct during the preceding year. See

ante, at 8.

This approach also has a textual integrity that the

Court’s reading does not: It gives “term of imprisonment”

the same meaning each time it is used by the statute.

Every time it appears in §3624(b)(1), “term of imprison

ment” refers to the administrative period that a prisoner

must complete in order to earn his freedom. The Court, by

contrast, would read this phrase to mean “time actually

served” the third time it is used, but “the sentence im

posed” the first two times it is used (“ ‘a prisoner who is

serving a term of imprisonment of more than 1 year[,]

other than a term of imprisonment for the duration of the

prisoner’s life’ ”). See ante, at 8–9. The Court’s interpreta

tion thus runs afoul of the “ ‘presumption that a given

term is used to mean the same thing throughout a stat

ute.’ ” Ante, at 9 (quoting Brown v. Gardner, 513 U. S.

115, 118 (1994)). The inconsistency here is particularly

Cite as: 560 U. S. ____ (2010) 5

KENNEDY, J., dissenting

egregious because all three uses appear in the same sen

tence. See id., at 118 (“[The] presumption [is] surely at its

most vigorous when a term is repeated within a given

sentence”).

The Court responds by noting another part of the stat

ute, a provision stating that prisoners shall receive cloth

ing, money, and transportation “[u]pon the release of [the]

prisoner on the expiration of the prisoner’s term of impris

onment.” §3624(d). A prisoner is released at the end of

his actual time behind bars, says the Court, and so “term

of imprisonment” must here refer to time actually served.

Yet release also comes at the end of a prisoner’s “term” in

the sense described above—that is, when the balance of

the sentence has been reduced to zero through a combina

tion of prison time and good time credits. Indeed, this

administrative use of the phrase fits well with the word

“expiration,” which in its most natural sense in this con

text refers to the close of a formal accounting period. See

Black’s Law Dictionary 619 (8th ed. 2004) (“A coming to

an end; esp., a formal termination on a closing date”). By

contrast, it is awkward at best to say, as the Court would

have it, that a prisoner’s actual time behind bars is some

thing that “expires.”

The Court’s approach produces yet another oddity. The

statute requires that prorated credit be awarded for “the

last year or portion of a year of the term of imprisonment.”

One might naturally assume that the last year of a ten

year term would be year ten. That is how things work

under the approach described above, in which a ten-year

sentence is subdivided into ten administrative segments.

But under the Court’s reading, a prisoner serving a ten

year sentence will never reach year ten of his term; year

ten simply does not exist. According to the Court, year

nine is the final year, and even year nine is not a full year:

It lasts “no more than 298 days.” Ante, at 3. If this

sounds confusing, it will be all the more so to the prisoner

6 BARBER v. THOMAS

KENNEDY, J., dissenting

who has just received his sentence and turns to the statute

books to figure out when to expect his freedom.

The Court does not even attempt to defend these flaws.

Instead, it points to four supposed defects in the approach

described above. None withstands examination.

First, the Court notes that the statute requires the

release of a prisoner “upon ‘the expiration of the prisoner’s

term of imprisonment, less any time credited’ for good

behavior.” Ante, at 15 (quoting §3624(a)). But if “term of

imprisonment” truly refers to the entire span that a pris

oner must complete to earn his freedom—a period that

accounts both for actual time and for good time credits—

then why would the “less any time credited” language be

appropriate? The answer is that this provision—which

appears at the very beginning of the section entitled “Re

lease of a prisoner”—announces to a prisoner when release

may be expected: when the prisoner’s term expires, taking

into account credit days “as provided in subsection (b).”

§3624(a) (bold face deleted). This use of language is com

mon. A debtor who says “I will write a check for what I

owe you, less what you owe me” is simply saying “I will

pay what I owe, taking into account your debts to me.”

Perhaps the same meaning could have been conveyed

using different words, but this is hardly probative.

Second, the Court alleges that the above approach con

flicts with the statute’s requirement that credit be

awarded “at the end of each year” based upon behavior

“during that year.” After all, if a year of the term can be

satisfied in part through credit, then it may last less than

a full calendar year. Yet the statute does not require that

credit be awarded at the end of a calendar year for good

behavior during a calendar year. What it requires is that

credit be awarded “at the end of each year of the prisoner’s

term of imprisonment” for good behavior “during that

year.” And this is precisely what the above approach does.

Third, the Court frets that, under the approach above,

Cite as: 560 U. S. ____ (2010) 7

KENNEDY, J., dissenting

prisoners will earn credit at different rates during a single

sentence. It admonishes that “[t]he use of different rates

finds no support in the statute.” Ante, at 16. This re

sponse is telling. The statute, in fact, prescribes no par

ticular rate—and certainly no formula based on a rate—

except as embodied in one clear directive: Prisoners are

eligible to earn “up to 54 days at the end of each year of

the prisoner’s term of imprisonment.” As to that com

mand, the above approach is perfectly faithful.

Fourth, the Court suggests that the above approach

causes credit to vest immediately, contrary to the statute.

Again, this is not true. As per the statute, credit only

vests “on the date the prisoner is released from custody,”

§3624(b)(2), meaning that it can be revoked at any time

before that date. This gives prisoners approaching their

release date an extra incentive to behave.

As a fallback, the Court wonders what would happen if

a prisoner misbehaved on the final day of his ten-year

sentence. Would the Bureau of Prisons (BOP) be forced to

“retroactively adjust the duration of all of his [term years]

to 365 days”? Ante, at 17. The answer is what one might

suppose: A prisoner whose credits are revoked will find

himself precisely where he would have been if those cred

its had never been earned. All years of the term remain

365 days, as they always have. But a misbehaving pris

oner who had formerly earned, say, 500 credits will find

himself without the benefit of those 500 days. That will

leave him with more of his term to complete—500 days

more, to be precise. If he behaves well again, he can re

sume earning credit for the remainder of his term, but he

has lost the opportunity to earn credits for any prior years.

See §3624(b)(1). This is not at all confusing for a prisoner;

and certainly it is as straightforward, if not more so, than

the Court’s approach. The Court’s view causes a prisoner’s

“term of imprisonment” to shrink over time according to

an algebraic formula, only to expand again if he misbe

8 BARBER v. THOMAS

KENNEDY, J., dissenting

haves.

Finally, the Court speculates that BOP might find the

above approach difficult to administer. The Court identi

fies no basis for this claim, nor does one exist. The infor

mation used to calculate a prisoner’s term under the above

approach is the same as it is under the Court’s approach.

True, a prisoner may become eligible to be awarded credit

on different calendar days during the course of his term.

But under the Court’s approach, this also happens when

awarding credit in the final year. And, it goes without

saying, federal prisoners begin their incarceration on

different calendar days anyway, so that under any ap

proach, BOP will be forced to evaluate prisoners through

out the calendar year.

II

The Court’s reading of §3624(b)(1), therefore, is less

consistent with the text than the reading explained above.

But even if these interpretations were in equipoise, under

any fair application the rule of lenity should tip the bal

ance in petitioners’ favor. When a penal statute is suscep

tible of two interpretations, the one more favorable to the

defendant must be chosen unless “text, structure, and

history . . . establish that the [harsher] position is unam

biguously correct.” United States v. Granderson, 511 U. S.

39, 54 (1994). Resolving ambiguity in favor of lenity en

sures that statutes provide “fair warning[,] . . . in language

that the common world will understand, of what the law

intends to do if a certain line is passed.” United States v.

Bass, 404 U. S. 336, 348 (1971) (internal quotation marks

omitted). The rule thus applies “not only to interpreta

tions of the substantive ambit of criminal prohibitions, but

also to the penalties they impose.” Bifulco v. United

States, 447 U. S. 381, 387 (1980).

The Court assumes without deciding that §3624(b) is

penal in nature. See ante, at 13. No assumption is neces

Cite as: 560 U. S. ____ (2010) 9

KENNEDY, J., dissenting

sary: The statutory provision awarding good time credits

“in fact is one determinant of [a] prison term,” so that a

prisoner’s “effective sentence is altered once this determi

nant is changed.” Weaver v. Graham, 450 U. S. 24, 32

(1981). In Weaver, the Court considered whether an

amendment to Florida’s statutory formula for calculating

good time credits implicated the Ex Post Facto Clause.

The Court concluded that it did, as the new statute “sub

stantially alter[ed] the consequences attached to a crime

already completed, and therefore change[d] ‘the quantum

of punishment.’ ” Id., at 33 (quoting Dobbert v. Florida,

432 U. S. 282, 294 (1977)). For the same reason, the penal

effect of §3624(b)(1) is substantial enough to implicate the

rule of lenity. We should not disadvantage almost 200,000

federal prisoners unless Congress clearly warned them

they would face that harsh result.

III

The Government—although not the Court—argues that

we should embrace its interpretation out of deference to

BOP. BOP has been charged by the Attorney General

with responsibility for “[a]pproving inmate disciplinary

and good time regulations.” 28 CFR §0.96(s) (2009). BOP

has long followed the same credit-calculation method now

advocated by the Court. The Government argues that we

should defer to BOP’s choice as a permissible exercise of

its delegated responsibility.

This argument fails on multiple levels. There is no

indication that BOP has exercised the sort of interpretive

authority that would merit deference under Chevron

U. S. A. Inc. v. Natural Resources Defense Council, Inc.,

467 U. S. 837 (1984). The statute does not create a legis

lative gap for BOP to fill. To the contrary, the procedures

that govern the timing of credit awards are spelled out in

great detail. Cf. Lopez v. Davis, 531 U. S. 230, 241–242

(2001) (where statute says that BOP “may” grant early

10 BARBER v. THOMAS

KENNEDY, J., dissenting

release to certain prisoners, without specifying further

criteria, Congress deliberately created a “statutory gap”).

The statute even goes so far as to explain what to do “[i]f

the date for a prisoner’s release falls on a Saturday, a

Sunday, or a legal holiday.” §3624(a). This legislative

specificity as to timing contrasts with other provisions

that do delegate authority to BOP. E.g., §3624(b)(1)

(awarding of credit is “subject to determination” by BOP

that the prisoner “has displayed exemplary compliance

with institutional disciplinary regulations”).

BOP has not claimed that its view is the product of any

“formal administrative procedure tending to foster the

fairness and deliberation that should underlie a pro

nouncement” with the force of law. United States v. Mead

Corp., 533 U. S. 218, 230 (2001). In 2005, BOP made final

an administrative rule adopting its preferred methodology.

70 Fed. Reg. 66752 (adopting 28 CFR §523.20). But when

pressed during an earlier stage of this litigation, BOP

conceded that it had “failed to articulate in the adminis

trative record the rationale upon which it relied when it

promulgated” the rule. Tablada v. Thomas, 533 F. 3d 800,

805 (CA9 2008). The Court of Appeals accepted BOP’s

concession, ibid., and that aspect of its ruling has not been

appealed.

As a fallback position, the Government argues that

BOP’s interpretation should receive at least some defer

ence under Skidmore v. Swift & Co., 323 U. S. 134 (1944).

But under Skidmore, an agency decision only merits “re

spect proportional to its ‘power to persuade.’ ” Mead,

supra, at 235 (quoting Skidmore, supra, at 140). BOP’s

position is of long standing, but the administrative record

is noteworthy for what it does not contain—namely, any

reasoned justification for preferring BOP’s methodology

over statutorily permissible alternatives. BOP has consis

tently adhered to its mistaken belief that its approach is

the only one that can be squared with the text. See 62

Cite as: 560 U. S. ____ (2010) 11

KENNEDY, J., dissenting

Fed. Reg. 50786 (1997) (explanation to interim rule assert

ing that the correct methodology “had been clearly stated

by statute since the implementation of the Sentencing

Reform Act of 1984”). For example, at no point did BOP

consider, much less consciously reject, the interpretation

outlined here. Cf. Reno v. Koray, 515 U. S. 50, 60–61

(1995) (deferring to BOP’s reasoned decision to reject one

interpretation in favor of another). An agency need not

consider all possible alternatives. But deference is not

owed to an agency view, however consistently held, that

from the start has been premised on legal error. See

Mead, supra, at 228; Skidmore, supra, at 140.

* * *

The straightforward interpretation urged here accords

with the purpose of the statute, which is to give prisoners

incentive for good behavior and dignity from its promised

reward. Prisoners can add 54 days to each year. And

when they do so, they have something tangible. In place

of that simple calculation, of clear meaning, of a calendar

that can be marked, the Court insists on something differ

ent. It advocates an interpretation that uses different

definitions for the same phrase in the same sentence;

denies prisoners the benefit of the rule of lenity; and caps

off its decision with an appendix that contains an alge

braic formula to hang on a cell wall.

To a prisoner, time behind bars is not some theoreti

cal or mathematical concept. It is something real, even

terrifying. Survival itself may be at stake. See Dept.

of Justice, Bureau of Justice Statistics, C. Mumola,

Suicide and Homicide in State Prisons and Local

Jails (NCJ 210036, Aug. 2005), online at http://

bjs.ojp.usdoj.gov/content/pub/pdf/shsplj.pdf (all Internet

materials as visited June 2, 2010, and available in

Clerk of Court’s case file) (prison homicide rates); Na

tional Prison Rape Elimination Commission Re

12 BARBER v. THOMAS

KENNEDY, J., dissenting

port, p. 4 (June 2009) (citing a national survey estimating

that 60,500 state and federal prisoners had been sexually

abused during the preceding year). To this time, the

Court adds days—compounded to years. We should not

embrace this harsh result where Congress itself has not

done so in clear terms. I would reverse the judgment of

the Court of Appeals.