S-corporations and partnerships on a calendar year file by March 16, 2026. C-corporations file by April 15, 2026. Set a reminder now and you have months of buffer instead of a last-minute scramble.
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| S-corp (Form 1120-S) | March 16, 2026 |
| Partnership (Form 1065) | March 16, 2026 |
| Multi-member LLC (default partnership) | March 16, 2026 |
| C-corp (Form 1120) | April 15, 2026 |
| Single-member LLC (Schedule C) | April 15, 2026 (with personal return) |
| Extension form (Form 7004) | Due by original deadline |
| Extended S-corp / partnership | September 15, 2026 |
| Extended C-corp | October 15, 2026 |
Source: IRS Publication 509, Tax Calendars (2026 edition). Fiscal-year corporations file by the 15th day of the fourth month after their year-end, except for corporations with a June 30 year-end, which file by the 15th day of the third month.
March 15 is the statutory deadline for S-corporations and partnerships every year. In 2026 it falls on a Sunday, so the IRS rolls the deadline to the next business day. That makes the actual due date Monday, March 16, 2026. Filing on March 15 is technically early, not late — but most accounting software defaults to the official Monday date.
C-corporations are not affected this year. April 15, 2026 is a Wednesday and stands as the deadline without any shift. If you have a fiscal-year corporation, the same weekend rollover rule applies to your specific 15th-day deadline.
The dates shift slightly each year as the calendar moves underneath them. Here is the five-year picture, useful if you are filing late returns from prior years or planning ahead for next year.
| Tax year | S-corp / partnership | C-corp |
| 2024 returns (filed in 2025) | March 17, 2025 | April 15, 2025 |
| 2025 returns (filed in 2026) | March 16, 2026 | April 15, 2026 |
| 2026 returns (filed in 2027) | March 15, 2027 | April 15, 2027 |
| 2027 returns (filed in 2028) | March 15, 2028 | April 17, 2028 |
Most business owners know there is a deadline in mid-March or mid-April. What they do not have is a system that surfaces it 60 days in advance, when the lead time is still usable. By the first week of March, every reputable CPA in your area is at capacity, your books are not reconciled, and the K-1 source data is still scattered across email.
A reminder set today, in May, gives you ten months to handle the 2026 return calmly. It gives you eight months to handle a fiscal-year filing. And it gives you four months to handle the extended September deadline if you already filed Form 7004 for 2025.
Compare that to the alternative: $245 per shareholder per month if the S-corp return is late, plus 5% of unpaid tax per month on the C-corp return. The corporate tax filing reminder is the difference between those two numbers.
S-corporations on a calendar year file Form 1120-S by March 16, 2026. The statutory date is March 15, but it falls on a Sunday this year, so the deadline rolls to the next business day. Partnerships filing Form 1065 share the same March 16 deadline.
C-corporations on a calendar year file Form 1120 by April 15, 2026. Fiscal-year C-corps file by the 15th day of the fourth month after their year-end. Corporations with a June 30 year-end have a special deadline on the 15th day of the third month after year-end.
Yes. Filing Form 7004 by the original deadline extends the filing date by six months. The extended deadline is September 15, 2026 for S-corps and partnerships, and October 15, 2026 for C-corps. The extension covers filing only — any tax owed is still due on the original date.
In 2025, S-corporations and partnerships filed by March 17 (because March 15 fell on a Saturday). C-corporations filed by April 15. The extended deadlines were September 15, 2025 and October 15, 2025 respectively.
When March 15 or April 15 lands on a weekend or federal holiday, the IRS rolls the deadline forward to the next business day. This is why 2025 was March 17, 2026 is March 16, and 2027 returns to March 15. Some years also shift because of the Emancipation Day holiday in Washington, DC.
For the 2026 tax year, the four quarterly estimated payment dates are April 15, June 15, September 15, and January 15, 2027. These are separate from the annual return and apply mostly to C-corps and to S-corp shareholders or partners on their personal returns.
Free. No account. Get an email 60, 30, and 7 days before March 16 (or April 15) — and follow-ups until your return is filed.
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