S corporation return deadline: Form 1120-S
A calendar-year S corporation files Form 1120-S by March 15, or six months later with Form 7004. See the 2026 dates, the late penalty and the K-1 rule.
Prepared by Prem Tax and Accounting Corp. Last checked against official sources on October 29, 2026.
A calendar-year S corporation files Form 1120-S by the 15th day of the third month after year end, which is March 15, 2027 for tax year 2026. Filing Form 7004 gives an automatic six-month extension to file, to September 15, 2027. Each shareholder still has a personal return of their own.
- The rule: the 15th day of the 3rd month after the tax year ends. A due date on a weekend or legal holiday moves to the next business day.
- For tax year 2025 the due date was March 16, 2026, because March 15 fell on a Sunday.
- For tax year 2026 the date is Monday, March 15, 2027. With Form 7004 the extended date is Wednesday, September 15, 2027.
- Late filing costs a monthly penalty for each shareholder, up to 12 months.
- Shareholders report their share from Schedule K-1 on Form 1040.
The dates for a calendar-year S corporation
| Tax year | Form 1120-S due | Extended due date with Form 7004 |
|---|---|---|
| 2025 | March 16, 2026 | September 15, 2026 |
| 2026 | March 15, 2027 | September 15, 2027 |
The IRS says the return is due on the 15th day of the third month after the tax year ends. If the corporation uses a fiscal year, count three months from its own year end. The dates above are for a calendar year.
How the extension works
File Form 7004
The IRS describes Form 7004 as an automatic six-month extension for certain business returns. File it by the regular due date.
Use the new date
The six months add time to file the return, not time to pay any tax the corporation owes. Check the Form 7004 instructions for payment rules.
Send the K-1s with the return
Each shareholder needs a Schedule K-1 to finish a personal return, so an extended 1120-S often means an extended 1040 too.
What a late return can cost
For the 2025 instructions, the penalty for a return with no tax due is $255 for each month or part of a month, up to 12 months, multiplied by the number of people who were shareholders during the year. If the corporation owes tax, an extra charge of 5 percent of the unpaid tax per month applies, capped at 25 percent. A $340 penalty can apply to each Schedule K-1 that is not given to a shareholder on time or is wrong. These amounts are inflation-adjusted and can change, so check the current instructions.
What to do next
- Confirm that your S election is in effect and what your tax year end is.
- Put March 15 and, if needed, September 15 on your calendar and file Form 7004 early if the books are not done.
- Plan owner payroll and estimated tax too, covered in our startup tax planning guide.
This is general information for tax years 2025 and 2026, not advice for your company.
Common questions
Is the S corporation return due before my personal return?
Yes. The 1120-S is due March 15 for a calendar year, a month before the April 15 personal deadline.
Does Form 7004 extend the date to pay tax?
The extension is for filing. Read the Form 7004 instructions about paying any tax owed.
What if March 15 falls on a weekend?
The due date moves to the next business day. That happened for tax year 2025, when the date was March 16, 2026.
Do I file Form 1120-S online?
An S corporation that must file 10 or more returns in a year has to e-file its 1120-S. Many others choose to.
Official sources
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