A calendar year S corporation must file Form 1120-S by March 15, which makes the S corp tax return due date for the 2025 tax year Monday, March 16, 2026, because March 15 falls on a Sunday. Fiscal year filers use the same formula: the return is due on the 15th day of the third month after the tax year ends. Filing on time protects the corporation from a per-shareholder monthly penalty and gets Schedule K-1s into shareholders’ hands in time for their April 15 personal returns.
Calendar Year Deadline
The standard federal deadline for Form 1120-S is the 15th day of the third month after the close of the tax year. For a January-through-December filer, that is March 15. When March 15 falls on a Saturday, Sunday, or federal holiday, the deadline shifts to the next business day.1Internal Revenue Service. Instructions for Form 1120-S For the 2025 tax year, that pushes the due date to March 16, 2026.
Check the calendar before assuming March 15 is the actual date each year. The IRS publishes an annual tax calendar in Publication 509 listing the adjusted deadlines.2Internal Revenue Service. Publication 509 (2026), Tax Calendars
Fiscal Year and Short Year Deadlines
S corporations that operate on a fiscal year use the same rule: the return is due on the 15th day of the third month after the fiscal year closes.3Internal Revenue Service. Starting or Ending a Business 3 Two common examples:
- Fiscal year ending June 30: return due September 15.
- Fiscal year ending September 30: return due December 15.
The weekend-and-holiday rule applies the same way. A short tax year, whether caused by a change in accounting period or a mid-year dissolution, follows the same formula: count three months from the day the short year ends and file by the 15th of that month.
Schedule K-1 Delivery to Shareholders
The S corporation must give each shareholder a Schedule K-1 on or before the day Form 1120-S is due.1Internal Revenue Service. Instructions for Form 1120-S For a calendar year corporation filing for tax year 2025, that means K-1s should reach shareholders by March 16, 2026. Shareholders need them to report their share of income, deductions, and credits on personal returns typically due April 15.
If the corporation extends its return, the K-1 delivery date extends with it. Shareholders who do not have their K-1s in hand by mid-April often need to file their own individual extensions on Form 4868.
Failing to deliver a correct K-1 on time can trigger a separate information-return penalty. The base amount is $250 per statement, adjusted annually for inflation.4eCFR. 26 CFR 301.6722-1 – Failure to Furnish Correct Payee Statements
Filing an Extension With Form 7004
A corporation that cannot complete its return by the original deadline can file Form 7004 for an automatic six-month extension.5Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time to File Certain Business Income Tax, Information, and Other Returns Form 7004 asks for the corporation’s legal name, address, EIN, and tax year. It has to be submitted on or before the original due date. A request filed one day late is invalid.
The extension gives you more time to file, not more time to pay.6Internal Revenue Service. Instructions for Form 7004 Most S corporations owe no entity-level tax, but a corporation that owes built-in gains tax, excess net passive income tax, or LIFO recapture tax must remit those amounts by the original due date.7Internal Revenue Service. Instructions for Form 1120-S (2025) Interest accrues on any unpaid balance from that original date regardless of the extension.
For a calendar year filer, a valid Form 7004 moves the deadline to September 15. September 15, 2026, falls on a Tuesday, so no further shift applies for the 2025 tax year return. The IRS does not send a separate approval notice; keep the e-file confirmation or a copy of the mailed form as proof.
Estimated Payments When Entity-Level Tax Applies
If the corporation owes built-in gains tax or excess net passive income tax, it must make quarterly estimated payments on the 15th day of the 4th, 6th, 9th, and 12th months of its tax year.2Internal Revenue Service. Publication 509 (2026), Tax Calendars For a calendar year filer in 2026, those dates are April 15, June 15, September 15, and December 15. The payment deadlines apply even if the corporation has filed an extension for its return.
Late Filing Penalty
Missing the deadline without a valid extension triggers a penalty under IRC 6699. The IRS charges it for each month or partial month the return is late, up to 12 months, and multiplies the monthly amount by the number of shareholders in the corporation during any part of the tax year.8Office of the Law Revision Counsel. 26 USC 6699 – Failure to File S Corporation Return
For returns due in 2026 (2025 tax year), the per-shareholder monthly amount is $255.9Internal Revenue Service. Failure to File Penalty A corporation with 10 shareholders that files three months late owes $7,650 ($255 × 10 × 3). At the 12-month maximum, the same corporation owes $30,600. For returns due in 2027 (2026 tax year), the per-shareholder amount rises to $260.10Internal Revenue Service. Rev. Proc. 2025-32
If entity-level tax is also owed and not paid on time, a separate failure-to-pay penalty applies under IRC 6651 at 0.5% of the unpaid tax per month, up to 25%.11Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax Interest runs on any unpaid balance from the original due date.
Getting a Late Filing Penalty Reduced
Two main paths can reduce or eliminate an assessed penalty.
First Time Abate Waiver
The IRS offers an administrative waiver for corporations with a clean compliance history. To qualify, the corporation must have filed Form 1120-S for the three preceding tax years with no unreversed penalties, other than estimated tax penalties, during that look-back.12Internal Revenue Service. IRM Part 20.1.1 Introduction and Penalty Relief The waiver covers late filing but not penalties for a return that is missing required information.13Internal Revenue Service. IRM Part 20.1.2 Failure to File/Failure to Pay Penalties
Reasonable Cause
A corporation that does not qualify for First Time Abate can ask for relief by showing the late filing was due to reasonable cause and not willful neglect. The IRS accepts several circumstances, including:
- Natural disasters or fires that destroyed records.
- Inability to obtain records needed to complete the return.
- Death, serious illness, or unavoidable absence of a key person.
- System issues that prevented a timely electronic filing.
The IRS has stated that relying on a tax professional, making an honest mistake, or lacking funds to pay a preparer generally do not qualify as reasonable cause on their own.14Internal Revenue Service. Penalty Relief for Reasonable Cause Each request turns on the specific facts, and the corporation must show it exercised ordinary business care.
Final Return After Dissolution
A dissolving or liquidating S corporation must file a final Form 1120-S by the 15th day of the third month after the date it dissolved.1Internal Revenue Service. Instructions for Form 1120-S A corporation that dissolves on August 10 has a final return due by November 15. Check the “final return” box on the form.
Separately, the corporation must file Form 966 within 30 days after adopting a resolution or plan to dissolve.15Internal Revenue Service. Form 966 Corporate Dissolution or Liquidation If the dissolution plan is later amended, a new Form 966 is due within 30 days of the amendment. Final K-1s go to shareholders on the same schedule as the final return, and the per-shareholder monthly penalty applies the same way if the final return is late.