Iowa Code § 321.127: Payment of refund.

1. The refund of the annual registration fee for vehicles shall be computed on the basis of the number of unexpired months remaining in the registration year from date of filing of the claim for refund with the county treasurer, computed to the nearest dollar.

2. The department, unless reasonable grounds exist for delay, shall make refund on or before the last day of the month following the month in which the claim is filed with the department.

3. For trailers or semitrailers issued a permanent registration plate, a refund shall be paid equal to the annual fee for twelve months times the remaining number of complete registration years.

4. Refunds for vehicles registered for apportioned registration under chapter 326 shall be paid on the basis of unexpired complete calendar months remaining in the registration year from the date the claim for refund and the license plate are received by the department.