Iowa Code § 421.9A: Due dates and holidays.

1. As used in this section, “holiday” means any of the following:

a. A legal public holiday as described in section 1C.1.

b. A paid holiday as described in section 1C.2, subsection 1, and subsection 2, paragraph “b”.

c. A federal holiday observed by the United States postal service.

d. A banking holiday observed by the federal reserve.

e. A date when the office of the department is otherwise closed pursuant to section 4.1, subsection 34.

2. When the due date for filing a return or other document with the department or the due date for the department to take any action falls on a Saturday, Sunday, or any holiday, the act is considered to be performed timely if the act is performed on or before the first business day following the Saturday, Sunday, or holiday.