Deadlines
S corp tax deadline: when Form 1120-S is due and how to extend it
Form 1120-S is due the 15th day of the 3rd month after the tax year ends (March 16, 2026 for 2025 calendar-year returns). See the Form 7004 extension, estimated tax dates, the Form 2553 deadline and the 2026 and 2027 late-filing penalties.
Prepared by Aldro Accounting · Updated · Sources checked
The quick answer
An S corporation files Form 1120-S by the 15th day of the 3rd month after its tax year ends, which is March 15 for a calendar-year corporation, moved to the next business day when it falls on a weekend or legal holiday. The IRS set March 16, 2026 for 2025 calendar-year returns because March 15 fell on a Sunday. Form 7004, filed by that date, extends the time to file, generally by 6 months, but not the time to pay.
When Form 1120-S is due
Generally, an S corporation must file Form 1120-S by the 15th day of the 3rd month after the end of its tax year. For calendar-year corporations filing 2025 returns, the IRS instructions give March 16, 2026, because March 15 fell on a Sunday.
Scroll sideways to see all columns.
| Tax year | Form 1120-S due | Why |
|---|---|---|
| 2025 | March 16, 2026 | March 15, 2026 fell on a Sunday (IRS instructions) |
| Any calendar year | March 15 of the next year | Moved to the next business day if it is a weekend or legal holiday |
When a due date falls on a Saturday, Sunday or legal holiday, the corporation can file on the next day that isn't a Saturday, Sunday or legal holiday. So for a calendar-year corporation the date is March 15 unless that day is a weekend or holiday.
A fiscal-year S corporation counts from its own year end. A corporation that dissolved generally files by the 15th day of the 3rd month after the date it dissolved. An S corporation making a section 336(e) election generally files by the 15th day of the 3rd month after the qualified stock disposition.
Extending the deadline with Form 7004
Form 7004 asks for an extension of time to file. Generally, it must be filed by the regular due date of Form 1120-S. Filing it properly gives the maximum extension allowed, and the automatic extension period is generally 6 months.
Form 7004 does not extend the time to pay. Any tax due is generally payable in full by the return's original due date, not including extensions. The Form 7004 instructions add that a corporation granted an extension isn't charged a late payment penalty if the tax paid by the regular due date is at least 90% of the total tax on the return and the rest is paid by the extended due date.
What an S corp actually pays by the deadline
The Form 2553 instructions say the income of an S corporation generally is taxed to its shareholders rather than to the corporation. The corporation pays tax itself on a short list of items. If its tax on built-in gains, excess net passive income tax and investment credit recapture tax total $500 or more, it makes estimated tax installments.
For a calendar-year corporation, the 2026 installments are due April 15, June 15, September 15 and December 15. A fiscal-year corporation pays by the 15th day of the 4th, 6th, 9th and 12th months of its year. Payments go by electronic funds transfer. EFTPS accepts same-day payments of $1 million or less submitted before 3:00 p.m. Eastern time on a business day.
Penalties for missing the S corp deadline
An S corporation can owe a late-filing penalty even when it owes no tax, because the penalty is figured per shareholder. The amounts below are from the Form 1120-S instructions for returns due in 2026 and Rev. Proc. 2025-32 for returns due in 2027.
If the corporation gets a penalty notice after filing, it can send the IRS an explanation to see if it meets reasonable-cause criteria. The instructions say not to attach that explanation to the return.
The Form 2553 election deadline
Form 1120-S is only for corporations whose S election was filed on Form 2553, accepted by the IRS and still in effect. The instructions say not to file Form 1120-S unless the corporation has filed or is attaching Form 2553.
Form 2553 is due no more than 2 months and 15 days after the beginning of the tax year the election is to take effect, or at any time during the tax year before. The IRS generally sends a determination within 60 days. Late election relief under Rev. Proc. 2013-30 generally needs reasonable cause and filing within 3 years and 75 days of the effective date on line E of the form.
Revoking works on a similar clock. A revocation with no date specified takes effect at the start of the tax year if made on or before the 15th day of the 3rd month of that year, and at the start of the next tax year if made later.
Schedules K-1, K-2, K-3 and e-filing
Schedule K-1 must be provided to each shareholder on or before the day Form 1120-S is required to be filed. Schedules K-2 and K-3 are attached to Form 1120-S and filed by its due date, including extensions, and Schedule K-3 goes to shareholders on the same timeline as Schedule K-1. S corporations with total receipts and year-end total assets both under $250,000 no longer have to file Schedules K-2 and K-3. Under the K-2 and K-3 filing exceptions, the latest 1-month date for 2025 calendar-year corporations that extend is August 17, 2026.
S corporations that file 10 or more returns of any type during the calendar year must e-file Form 1120-S.
Aldro's flat yearly price covers everything tax for the year, including Form 1120-S, extensions and the state returns. Our team prepares and files them.
Worked example
Say a calendar-year S corporation with three shareholders owes no tax and files its 2025 Form 1120-S on June 1, 2026 without an extension. It is late from March 16 through June 1, which counts as 3 months or parts of a month. The penalty is $255 times 3 months times 3 shareholders, or $2,295. Filing Form 7004 by March 16, 2026 would have moved the filing date out by the automatic extension instead. For a return due in 2027, the same lateness would be $260 times 3 times 3, or $2,340.
Common questions
When is the S corp tax deadline for 2026?
Form 1120-S for 2025 calendar-year S corporations was due March 16, 2026, because March 15 fell on a Sunday. The rule is the 15th day of the 3rd month after the tax year ends.
How long is an S corp extension?
Form 7004, filed by the regular due date, gives an automatic extension that is generally 6 months. It extends the time to file, not the time to pay.
What is the penalty for filing an S corp return late?
For returns due in 2026, $255 per shareholder for each month or part of a month late, up to 12 months, even with no tax due. Returns due in 2027 use $260.
When is the deadline to elect S corp status?
Form 2553 is due no more than 2 months and 15 days after the start of the tax year the election should take effect, or any time in the tax year before.
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Sources
- IRS: Instructions for Form 1120-S · checked October 31, 2026
- IRS: Instructions for Form 7004 · checked October 31, 2026
- IRS: Instructions for Form 2553 · checked October 31, 2026
- IRS: Instructions for Form 1120-S (2023) · checked October 31, 2026
- IRS: Rev. Proc. 2025-32 · checked October 31, 2026
This guide explains general rules from the sources listed. It isn’t tax advice for your situation.