42-004: IA 1120S Income Tax Return for S Corporations 42-004 (2025)
Iowa · Iowa DOR · Used for tax years 2025
The 2025 IA 1120S is Iowa’s income tax return for S corporations. It reports corporation and shareholder information, income and deductions, Iowa adjustments, and Iowa-source distributive items.
Who files this form
The IA 1120S is Iowa’s income tax return for S corporations. This version covers calendar year 2025 or another fiscal year entered on the return.
The form does not state the full rules for which S corporations must file.
What you'll need
- Federal return: Include a complete copy of your federal return, excluding federal K-1s. Part 4 uses amounts from federal Form 1120-S and federal Schedule K.
- Business information: Have the corporation’s legal name, address, FEIN, NAICS code, shareholder counts, and pass-through representative information ready.
- Receipts information: Schedule E requires Iowa receipts and receipts everywhere to calculate the Business Activity Ratio (BAR).
- Payment information: Schedule C asks for estimated tax payments, credit from the prior period, voucher payments, and other payments. Include a statement for other payments.
Additional attachments depend on your return:
- Include IA 102 with an amended return.
- Include Schedule DE if reporting income from disregarded entities.
- Include Schedule D for nonbusiness income reported on Part 4, lines 22 and 26.
- Include supporting schedules for remaining Iowa net operating loss or credit carryforwards from C corporation years.
- Include Schedule CC for composite and PTET credits.
- Include IA 103 if making the audit election to pay on behalf of shareholders.
- Include IA 2220 for the underpayment of estimated tax penalty reported on line 49.
How to file
The form allows e-filing or mailing and notes that you may be required to file electronically.
Mail your return to:
Corporation Tax Return Processing
Iowa Department of Revenue
PO Box 10468
Des Moines, IA 50306-0468
Include a complete copy of your federal return, excluding federal K-1s, and any required attachments.
Sign the return by hand or with a digital signature that has a digital certificate. Stamped or typed signatures are not accepted.
Do not email your return. Forms and schedules are available at revenue.iowa.gov.
Common mistakes
- Leaving Schedule E blank: The form says the Business Activity Ratio schedule must be completed.
- Omitting required attachments: An amended return must include IA 102. A complete federal return, excluding federal K-1s, must accompany this return.
- Using a typed or stamped signature: Only a handwritten signature or a digital signature with a digital certificate is accepted.
- Assuming no tax due means no late filing penalty: The form warns that a late filing penalty may apply even if no tax is due.
- Completing Part 6 without a PTET election: Check the box and complete Part 6 only if the corporation has elected, or is electing, entity-level taxation for the tax year. The election is irrevocable.
- Emailing the return: The form specifically says not to email it.
Questions people ask
Can an overpayment be refunded or applied to the next return?
Yes. Line 52 lets you apply part or all of the overpayment to the next period’s return. Line 53 reports the amount to be refunded.
Can the corporation revoke its PTET election?
No. The form states that the pass-through entity tax (PTET) election is irrevocable.
What if the corporation reports income from disregarded entities?
Answer the question in Part 3 and include Schedule DE with the return.
Can someone else discuss the return with the Department?
The form has a Third Party Disclosure Designee section where you can indicate whether to allow an individual to discuss the return with the Department. It directs you to the instructions for details.
Where can I ask questions about the form?
Call 515-281-3114 or 800-367-3388, or email idr@iowa.gov. Do not email your return.