For ordinary calendar-year entities filing 2025 federal returns during 2026, Forms 1065 and 1120-S were due March 16, 2026 and are generally due September 15, 2026 with a timely, valid six-month extension. Form 1120 was due April 15, 2026 and is generally due October 15, 2026 with a timely, valid six-month extension.
2026 business tax deadline quick reference
These are federal deadlines for ordinary domestic calendar-year entities filing 2025 returns during calendar year 2026. The March dates shown already reflect the 2026 weekend adjustment.
- Partnership — Form 1065: March 16, 2026 regular deadline; September 15, 2026 with a timely, valid extension
- S corporation — Form 1120-S: March 16, 2026 regular deadline; September 15, 2026 with a timely, valid extension
- C corporation — Form 1120: April 15, 2026 regular deadline; October 15, 2026 with a timely, valid extension
These dates are for 2025 returns filed in 2026
A search for a “2026 business tax deadline” can refer either to a return filed during 2026 or to a return for tax year 2026. This page focuses on calendar-year 2025 returns filed during 2026 because those are the current filing and extension deadlines.
For ordinary calendar-year 2026 returns filed in 2027, Forms 1065 and 1120-S are generally due March 15, 2027, and Form 1120 is generally due April 15, 2027. With timely, valid six-month extensions, the general filing dates are September 15, 2027 and October 15, 2027, respectively.
Partnership and S corporation returns share a March deadline
A calendar-year partnership generally files Form 1065 by the 15th day of the third month after year-end. Because March 15 fell on a Sunday in 2026, the federal deadline for the 2025 return moved to Monday, March 16, 2026. A calendar-year S corporation follows the same general timing for Form 1120-S.
A properly completed Form 7004 filed by the regular return deadline generally provides a six-month filing extension to September 15, 2026. The applicable Schedule K-1 and Schedule K-3, when required, generally follow the filing deadline for the entity return, including a valid extension.
C corporations generally have an April deadline
An ordinary calendar-year C corporation generally files Form 1120 by the 15th day of the fourth month after year-end. For a 2025 calendar-year return, that date was April 15, 2026. A timely, valid Form 7004 generally extends the filing deadline to October 15, 2026.
Fiscal-year corporations can have different dates. A corporation with a tax year ending June 30 is subject to a special filing rule, and short-year, dissolved, foreign, or consolidated entities may also need a separate deadline analysis.
Form 7004 generally extends filing, not payment
Form 7004 is an application for an automatic extension of time to file certain business returns. It generally must be filed by the regular due date, include a proper estimate when applicable, and satisfy the form instructions. It does not generally extend the time to pay tax that is due.
Do not assume a partnership or S corporation can never owe entity-level federal tax. Certain taxes, elections, adjustments, and special situations can create an entity payment even when most income normally passes through to owners. State payment and extension rules can also differ from the federal rules.
Why the K-1 timetable matters to owners
Partners and S corporation shareholders generally need the entity’s Schedule K-1 to complete their own returns accurately. If the business return is extended, the owner and the preparer should coordinate what information is available, whether the owner’s return also needs an extension, and how estimates should be handled while final entity amounts are pending.
An entity extension is separate from an owner’s individual filing extension. It also does not automatically extend any state return, payment, election, payroll filing, or information return not covered by Form 7004.
State deadlines and extensions may be different
A federal extension does not establish one nationwide state rule. Some states accept the federal extension, some require a separate form or payment, and others use different deadlines or entity-level taxes. Multi-state businesses should review every filing jurisdiction rather than relying only on the federal calendar.
Disaster relief can change a deadline
An IRS disaster-relief notice may postpone filing and, in some cases, payment deadlines for eligible affected taxpayers. Relief depends on the declared disaster, covered location, taxpayer, form, and date. Check the specific IRS notice rather than assuming that a general news report applies to the entity.
Ordinary extensions and disaster postponements can interact. Confirm the later valid filing date and any separate payment date before relying on relief.
What to gather for a business-return review
- The entity type, tax year, states involved, and current filing status
- The prior federal and state returns and any extension confirmation
- Tax-ready financial statements, the general ledger, and year-end reconciliations
- Ownership changes, contributions, distributions, loans, and capital-account information
- Payroll, officer compensation, fixed assets, estimated payments, and major transactions
- The number of partners or shareholders and any K-1 or K-3 reporting needs
If the original deadline was missed
Do not assume that filing Form 7004 after the regular deadline will retroactively create a valid extension. Confirm whether an extension was timely accepted, whether disaster relief or another rule applies, and what return, payment, or notice response should be completed next.
Late-filing and late-payment consequences depend on the return, tax due, owners, timing, and available relief. Addressing a missed deadline promptly usually preserves more options than waiting for an agency notice.