Partnership and S-Corp returns: March 16, 2026. C-Corp and Schedule C returns: April 15. Extensions push everything to mid-September or mid-October. Quarterly estimates run on their own clock. Here's the full grid.
Calendar-year filers. Fiscal-year entities follow the same "3rd or 4th month" pattern shifted to their year-end.
| Entity | Form | Due date | Extended |
|---|---|---|---|
| Partnership (general, LP, LLP) | 1065 | March 16, 2026 | September 15, 2026 |
| Multi-member LLC (default) | 1065 | March 16, 2026 | September 15, 2026 |
| S-Corporation | 1120-S | March 16, 2026 | September 15, 2026 |
| LLC taxed as S-Corp | 1120-S | March 16, 2026 | September 15, 2026 |
| C-Corporation (calendar year) | 1120 | April 15, 2026 | October 15, 2026 |
| LLC taxed as C-Corp | 1120 | April 15, 2026 | October 15, 2026 |
| Single-member LLC (default) | Schedule C w/ 1040 | April 15, 2026 | October 15, 2026 |
| Sole proprietor | Schedule C w/ 1040 | April 15, 2026 | October 15, 2026 |
| Nonprofit (calendar year) | 990 | May 15, 2026 | November 16, 2026 |
March 15, 2026 falls on a Sunday, so the deadline shifts to Monday March 16. April 15 is a Wednesday and falls on the actual date.
Form 1065 is due by the 15th day of the third month after year-end. For calendar-year filers, that\'s March 15, pushed to March 16, 2026 because the 15th is a Sunday. Schedule K-1s must reach each partner or member by the same date.
Form 7004 gives an automatic 6-month extension to September 15, 2026. The partnership itself usually owes no federal tax (income passes through to partners), but missing the return triggers a per-partner late-filing penalty of $245 per month per partner, capped at 12 months. A 5-partner LLP that files three months late owes $3,675.
Form 1120-S is due March 16, 2026 for calendar-year filers. Same 6-month extension as partnerships. K-1s go to shareholders by the same date so they can prepare their personal returns.
S-Corps that owe federal tax (built-in gains tax, excess net passive income tax) must pay by the original deadline. The late-filing penalty is $245 per shareholder per month, capped at 12 months. Reasonable cause relief is available but requires documentation.
A calendar-year C-Corp files Form 1120 by April 15, 2026. Fiscal-year C-Corps file by the 15th day of the fourth month after year-end. The exception: corporations with a June 30 year-end file by September 15 (the 15th of the third month after year-end), a legacy rule that hasn\'t been changed.
C-Corps owe federal tax at the entity level (flat 21%). Failure-to-file: 5% of unpaid tax per month, capped at 25%. Failure-to-pay: 0.5% per month. Extensions push the filing deadline to October 15, 2026, but tax owed is still due on the original date.
Anyone expecting to owe $1,000 or more in federal tax (or $500+ for C-Corps) must pay in quarterly. Missing a quarter triggers an underpayment penalty, calculated daily at the federal short-term rate plus 3%.
Each entity has at least four federal dates (annual return + four quarterly estimates), plus a separate state annual report on a different schedule entirely. Trying to track all of them mentally is the actual reason missed filings happen. See the state annual report dates page for the other half of the calendar, or return to the business filing reminders guide.
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For most calendar-year businesses, federal returns are due April 15, 2026. Partnerships and S-Corps file Form 1065 or 1120-S by March 16, 2026 (March 15 falls on a Sunday). C-Corps on a calendar year file Form 1120 by April 15. Sole proprietors file Schedule C with their personal Form 1040 by April 15.
It depends on how the LLC is taxed. A single-member LLC is a disregarded entity that files Schedule C with the owner's Form 1040 by April 15, 2026. A multi-member LLC files Form 1065 by March 16, 2026. An LLC that elected S-Corp treatment files Form 1120-S by March 16, 2026. An LLC that elected C-Corp treatment files Form 1120 by April 15, 2026.
An S-Corp must file Form 1120-S by the 15th day of the third month after the tax year ends. For a calendar-year S-Corp that's March 15 — pushed to March 16, 2026 because March 15 is a Sunday. K-1s must be issued to shareholders by the same date.
A C-Corp on a calendar year files Form 1120 by the 15th day of the fourth month after year-end, which is April 15, 2026. A C-Corp with a fiscal year ending June 30 has a special rule: the return is due the 15th day of the third month after year-end (September 15). All other fiscal-year C-Corps file by the 15th of the fourth month.
Partnerships and S-Corps file Form 7004 for a 6-month extension, pushing the deadline from March 16 to September 15, 2026. C-Corps and single-member LLCs filing Schedule C extend to October 15, 2026. An extension is an extension to file, not to pay. Any tax owed is still due on the original deadline.
Q1: April 15, 2026 (for income earned January 1 to March 31). Q2: June 15, 2026 (April 1 to May 31). Q3: September 15, 2026 (June 1 to August 31). Q4: January 15, 2027 (September 1 to December 31). C-Corps follow the same schedule using Form 1120-W.
No. State annual reports are completely separate from federal income tax returns. They go to the Secretary of State, not the IRS, and the dates vary wildly. California uses your formation anniversary month. Florida sets May 1 for everyone. Delaware sets June 1 for LLCs and March 1 for corporations. See our state-by-state annual report guide for the full list.
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