Returns filed during 2026 mostly report tax year 2025. Returns for tax year 2026 are generally filed in 2027. This guide covers both, plus C corporation, S corporation, fiscal-year, extension, state, and cross-border rules.
Key Takeaways
- Calendar-year C corporations (Form 1120) file by April 15, 2026.
- S corporations (Form 1120-S) file by March 16, 2026.
- Form 7004 extends the time to file, not the time to pay.
- Fiscal-year corporations count from their own year-end, not from March or April.
- Estimated taxes, payroll filings, information returns, and state taxes each run on separate calendars.
2026 Federal Corporation Tax Return Due Dates
The dates below apply to calendar-year corporations filing 2025 returns during 2026. They come from the IRS's Publication 509 and the 2025 return instructions.
| 2025 return | Original deadline | Extended deadline |
|---|---|---|
| C corporation, Form 1120 | April 15, 2026 | October 15, 2026 |
| S corporation, Form 1120-S | March 16, 2026 | September 15, 2026 |
Calendar-year C corporation deadline
Form 1120 is the federal income tax return for a C corporation. For a tax year that ended December 31, 2025, it is due April 15, 2026. Any tax balance is due the same day. A timely Form 7004 pushes the filing date to October 15, 2026, but not the payment date.
Calendar-year S corporation deadline
Form 1120-S is the S corporation return. March 15, 2026 falls on a Sunday, so the deadline moves to Monday, March 16, 2026 under the IRS weekend and holiday rule. The extended date is September 15, 2026.
An S corporation also prepares a Schedule K-1 for everyone who was a shareholder during the year. K-1s are due on the same schedule as the return. Entity-level tax, if any is owed, is also due March 16.
Filing mechanics and timing
- An e-filed return is not "filed" until the IRS acknowledges and accepts it.
- Rejected business returns generally get 10 calendar days to fix and resubmit (five days for Form 7004). That window is not an extension.
- A mailed return is generally timely if it carries a postmark on or before the due date and meets addressing and postage rules. Only designated private delivery services qualify, not every courier.
- Payments can go through IRS Direct Pay (free, from a bank account) or EFTPS.
- Any deadline falling on a Saturday, Sunday, or legal holiday moves to the next business day.
How Entity Type and Tax Year Affect the Deadline
The general rule is simple:
- C corporations: the 15th day of the fourth month after the tax year ends.
- S corporations: the 15th day of the third month after the tax year ends.
Apply the formula to your actual tax year, not to a calendar you assume.
Calendar-year corporations
A December 31, 2025 year-end gives a March 15 deadline for an S corporation (March 16, 2026) and April 15 for a C corporation. Those are returns filed in 2026.
The 2026 tax year, ending December 31, 2026, produces the same March and April dates in 2027, subject to weekend adjustments.
Fiscal-year corporations
Count from your year-end. Suppose a C corporation's year ends September 30, 2026. Its Form 1120 is due on the 15th day of the fourth month after that, which is January 15, 2027. An S corporation with the same year-end files Form 1120-S by December 15, 2026.
Confirm any date against the current instructions before relying on it.
Estimated tax payments shift with the fiscal year as well. They fall in the fourth, sixth, ninth, and twelfth months of the corporation's own tax year.
One transition rule matters here. C corporation years beginning before January 1, 2026 keep the old third-month deadline and a seven-month extension.
The IRS gives a short year ending June 30, 2026 as an example: its return is due September 15, 2026. Years beginning in 2026 use the fourth-month deadline and a six-month extension.
Short tax years and accounting-period changes
Several events create a short year or an unusual deadline:
- A new corporation's first, partial year (a C corporation generally files by the 15th day of the fourth month after it ends)
- Dissolution or liquidation, which ends the final period at dissolution
- Acquisitions that close out the target's tax year
- An approved change in accounting period via Form 1128
Automatic-approval Form 1128 applications are generally due with the short-period return, including extensions. Confirm exact dates with the IRS or a tax professional.
LLCs taxed as corporations
An LLC's legal form does not set its deadline. An LLC that elects corporate status (Form 8832) or is classified as a corporation generally follows Form 1120 rules. An LLC with an effective S election (Form 2553) follows Form 1120-S rules.
Estimated Tax Payments and Related Federal Filings
The annual return reports the year's tax. Estimated payments prepay that tax during the year. A C corporation generally must make them when expected tax, after credits, is $500 or more.
2026 C corporation estimated tax calendar
| Installment | Due date |
|---|---|
| First | April 15, 2026 |
| Second | June 15, 2026 |
| Third | September 15, 2026 |
| Fourth | December 15, 2026 |
These payments cover tax year 2026. They are separate from any balance due on the 2025 return in April. Underpayment is figured per installment on Form 2220, so a late catch-up payment may not erase the penalty. Form 1120-W is now historical.
How S corporation payments differ
S corporations generally pass income to shareholders. Shareholders may need their own estimated payments if they expect to owe $1,000 or more. The entity itself may owe estimates when built-in gains tax, excess net passive income tax, and investment-credit recapture together reach $500 or more. The same four dates apply.
Payroll and employment filings
Payroll deadlines are a separate track from income tax.
| Form | Key dates |
|---|---|
| 941 | Q4 2025: Feb 2, 2026. 2026: Apr 30, Jul 31, Nov 2; Q4 2026: Feb 1, 2027 |
| 940 | Feb 2, 2026 (2025); Feb 1, 2027 (2026) |
| W-2 | Feb 2, 2026 (2025); Feb 1, 2027 (2026) |
| 1099-NEC | Feb 2, 2026 (2025); Feb 1, 2027 (2026) |
The 2027 dates apply the January 31 rule with the next-business-day adjustment. Filing and deposit deadlines are different obligations, so check the IRS employment tax calendar for your deposit schedule.
Foreign-owned and information-reporting obligations
Not every foreign-owned corporation has the same duties. Form 5472 applies to a reporting corporation with reportable related-party transactions, generally a 25% foreign-owned US corporation or a foreign corporation engaged in a US trade or business. It is filed with the income tax return, including extensions.
A foreign-owned US disregarded entity files Form 5472 attached to a pro forma Form 1120 by the 1120 deadline. It must use fax or the special IRS mailing address, not e-file.
Extensions, Payments, and Late Filing Consequences
Form 7004 and the six-month extension
Corporations use Form 7004 to extend Forms 1120, 1120-S, 1120-F, and 1042. File it by the original due date.
Under the Form 7004 instructions, the automatic extension is six months. That yields September 15 for calendar-year S corporations and October 15 for C corporations. The June 30 transition rule above is the main exception.
An extension delays filing, not payment
Estimate your tax and pay it by the original due date. Interest runs on late-paid tax even when you have an extension. Underpaying also invites failure-to-pay penalties.
What happens after a missed deadline?
Current IRS rules include:
- C corporation failure to file: generally 5% of unpaid tax per month or part, up to 25%. For returns required in 2026 and more than 60 days late, the minimum is the smaller of $525 or the tax due.
- S corporation failure to file: $255 per month or part (up to 12 months) per shareholder, if no tax is due.
- Failure to pay: generally 0.5% of unpaid tax per month or part, up to 25%.
- Estimated-tax underpayment: calculated separately per installment.
If you miss a deadline, file as soon as possible and pay what you can. Then ask about relief.
The IRS describes reasonable cause relief for failures despite ordinary care. Lack of funds alone is not enough, and it does not cover estimated-tax penalties.
First Time Abate may also apply to eligible businesses with a clean record over the prior three years, including late S corporation returns.
State, Local, and Cross-Border Corporation Tax Considerations
State and local filing deadlines
State deadlines for income, franchise, gross receipts, sales, and payroll tax vary and may not match federal dates. Whether a federal extension carries over differs by state:
- Georgia: recognizes the approved federal extension without a separate application; attach Form 7004.
- California: offers its own automatic extension, and payment is not extended.
- New York: requires a separate request (CT-5, or CT-5.4 for S corporations) by the original state deadline.
Check your state revenue department before assuming anything.
Foreign corporations and US corporations with overseas operations
A US corporation with foreign activities files Form 1120, plus attachments. A foreign corporation with a US trade or business generally files Form 1120-F. Foreign ownership alone does not make a corporation foreign.
Form 1120-F is due the 15th day of the fourth month with a US office, or the sixth month without one. Related filings often track the parent return, though some have separate due dates:
- Forms 5471, 8858, 8938, and 8833 generally follow the parent return's deadline, including extensions
- FBAR (FinCEN 114) applies when foreign accounts exceed $10,000 in aggregate; for 2025 accounts due April 15, 2026 (auto-extended to October 15) via BSA E-Filing
- Forms 1042 and 1042-S report payments to foreign persons; for 2025, the March 15 date moves to March 16, 2026
- Transfer-pricing documentation must exist when the return is filed and be supplied within 30 days of an IRS request
Accounting and tax compliance support
No single deadline fits every company. VJM Global helps businesses organize accounting records, build tax compliance calendars, and coordinate cross-border reporting. That is particularly useful for US businesses with international operations or India-related activity. A short conversation about your entity type and year-end is usually enough to map out what applies to you.
Frequently Asked Questions
When are C corporation tax returns due in 2026?
Calendar-year C corporations file Form 1120 for tax year 2025 by April 15, 2026. A timely Form 7004 extends filing to October 15, 2026.
When is Form 1120-S due in 2026?
March 16, 2026, because March 15 is a Sunday. With a timely extension, the deadline is September 15, 2026.
What is the corporation tax extension deadline in 2026?
File Form 7004 by the original return deadline. The extended date depends on entity type and tax year: generally September 15 for S corporations and October 15 for calendar-year C corporations.
Does Form 7004 extend the time to pay corporate taxes?
No. It generally extends filing only. Tax is still due by the original deadline, and interest runs on late payments.
When are corporate estimated tax payments due in 2026?
Calendar-year C corporations pay on April 15, June 15, September 15, and December 15, 2026. These cover tax year 2026, separate from the annual return.
What happens if a corporation misses its tax return deadline?
Failure-to-file and failure-to-pay penalties plus interest can apply. File and pay as soon as possible, then ask a tax professional about reasonable cause or First Time Abate relief.
