Iowa runs on a distinctive April 30 calendar — later than the federal April 15 — for every entity, and it moved to a flat individual income tax for 2025. Its estimated-payment schedule is also unusual and easy to get wrong.

Iowa Tax Deadlines at a Glance (2026)

Every Iowa return is due the last day of the 4th month — April 30, 2026 — with an automatic six-month extension to October 31, provided at least 90% of tax is paid by April 30. Note that Iowa pass-throughs (April 30) are due roughly six weeks later than the federal March 15 date, not the one-month offset the individual comparison might suggest.

A New Flat Rate and Falling Corporate Tax

Iowa moved to a flat 3.8% individual income tax rate for 2025 (accelerated from graduated brackets by 2024 legislation). The corporate income tax is 5.5% on the first $100,000 and 7.1% above, on a revenue-triggered path down toward a flat 5.5%. Iowa’s elective pass-through entity tax is 3.8% and — thanks to recent federal law — is no longer scheduled to expire.

Iowa’s Unusual Estimated-Payment Dates

A common trap: Iowa individual estimated payments do not follow the federal schedule. They are due April 30, June 30, September 30, 2026, and January 31, 2027 — the end of each period, not the 15th. CPAs migrating clients from other states must reset these dates.

Extensions and Penalties

Iowa’s extension is automatic with no form, but it extends filing only — 90% of tax must be paid by April 30 to avoid the 10% failure-to-pay penalty. The 2026 interest rate is 10% per year (0.8% per month).

CPA Action Steps

• Use April 30 / October 31 for all Iowa returns

• Apply the flat 3.8% individual rate for 2025

• Reset estimated-payment dates to Iowa’s Apr 30 / Jun 30 / Sep 30 / Jan 31 schedule

• Pay 90% by April 30 to secure the extension and avoid penalty

Verify current rates and dates against the Iowa Department of Revenue (revenue.iowa.gov) before filing.