Miss. Code Ann. § 27-51-9

For the purposes of this chapter, the fiscal year shall commence on August 1 and shall end on July 31 of each year. The taxable year shall run concurrently with the taxable year in effect in the law pertaining to the payment of the road and bridge privilege license tax on motor vehicles. Except as otherwise provided in Section 27-41-2 , ad valorem taxes on motor vehicles shall be collected by the county tax collector for the county and state and by the municipal tax collector for the municipalities. Ad valorem taxes for any ensuing year may be paid during the month as provided in Section 27-19-31 , however, and said ad valorem taxes on any motor vehicle must be paid at the same time or prior to the time that the road and bridge privilege license is issued for the subject motor vehicle, unless herein otherwise specifically exempt from such ad valorem taxes. The ad valorem tax on motor vehicles shall be computed on the millage rates in effect at the time such privilege license tax is to be paid.