2 Computation of interest on unpaid tax. Interest shall accrue on tax due from the

original due date of the return. Interest on refunds of any portion of the tax imposed by statute which has been erroneously refunded and which is recoverable by the department shall bear interest as provided by law from the date of payment of the refund, with each fraction of a month considered to be an entire month. See rule 701—10.2(421) for the statutory interest rate. All payments shall be first applied to the penalty and then to the interest, and the balance, if any, to the amount of tax due. This rule is intended to implement Iowa Code sections 421.7 and 422.25. [Editorial change: IAC Supplement 11/2/22]