Iowa Administrative Code Title 701 — Department of Revenue
Iowa Admin. Code r. 701—306.4(422) — Computation of interest on overpayments
If the amount of tax determined to be due by the department is less than the amount paid, the excess to be refunded will accrue interest from the first day of the second calendar month following the date of payment or the date the return was due to be filed or was filed, whichever is the later.
Source: official text