Iowa Code § 384.2: Fiscal year and tax year.

1. Except as otherwise provided for special charter cities, a city’s fiscal year shall be as provided in section 24.2, subsection 3. All city property taxes must be certified by a city to the county auditor on or before April 30 of each year, unless otherwise provided by state law. However, municipal utilities, if not supported by taxation or the proceeds of outstanding indebtedness payable from taxes may, with the council’s consent, choose to operate on a fiscal year which is the calendar year. The receipt by the utility of payments from other governmental funds for public fire protection, street lighting, or other public use of the utility’s services shall not be deemed support by taxation. After notice and hearing in the same manner as required for the city’s regular budget under section 384.16, the utility budget must be approved by resolution of the council not later than twenty days prior to the beginning of the calendar year for which the budget applies.

2. The county auditor shall place city taxes and assessments upon the tax list for the current year, and the county treasurer shall collect city taxes and assessments in the same manner as other taxes. Delinquent city taxes and assessments draw the same interest as other taxes. Sales for delinquent city taxes and assessments must be made in the manner provided in chapter 446. The county treasurer shall combine in one tax sale all taxes and assessments due from the same person and collectible by the county.