S.D. Codified Laws § 32-9-17
Each commercial motor vehicle plate or validation decal, intrastate and interstate, shall be valid from the date of issue to the last day of the assigned expiration month. If any plate is issued after the renewal month, the commercial motor vehicle fee shall be paid only for the unexpired portion of the registration period. For each full month which has passed before the license is purchased there shall be a one-twelfth reduction of the annual commercial motor vehicle fee. If a vehicle is being commercially licensed for the first time and the registration expiration date falls within ninety days, the applicant may choose to make payment for the current period and for the succeeding period and receive a license for the next registration year.
SDCL 32-9-17