Deadlines
Corporate tax deadline: when Form 1120 is due, by year end
A C corporation's Form 1120 is due on the 15th day of the 4th month after its tax year ends: April 15 for calendar-year corporations. Due dates by fiscal year end, the June 30 exception and its 2026 change, Form 7004, estimated tax dates and penalties.
Prepared by Aldro Accounting · Updated · Sources checked
The quick answer
The IRS says a C corporation must generally file Form 1120 by the 15th day of the 4th month after its tax year ends, which is April 15 for a calendar-year corporation. Form 7004, filed by that date, gives an automatic 6-month extension to file (to October 15), but any tax is still due on the original date. Corporations with a June 30 year end have had a different rule, which changes for tax years beginning in 2026.
The general rule: 15th day of the 4th month
Generally, a corporation must file its income tax return by the 15th day of the 4th month after the end of its tax year. If the due date falls on a Saturday, Sunday or legal holiday, the corporation can file on the next business day.
Every domestic corporation, including one in bankruptcy, must file whether or not it has taxable income, unless it is exempt under section 501. An LLC or other domestic entity that elected to be taxed as a corporation files Form 1120 too.
Scroll sideways to see all columns.
| Tax year ends | Form 1120 due | Extended due date (6 months) |
|---|---|---|
| December 31 | April 15 | October 15 |
| March 31 | July 15 | January 15 |
| September 30 | January 15 | July 15 |
| June 30 | See the June 30 rules below | See the June 30 rules below |
C corporations file a month later than S corporations and partnerships. Form 1120-S and Form 1065 are due on the 15th day of the 3rd month after year end.
New and dissolved corporations
A new corporation filing a short-period return must generally file by the 15th day of the 4th month after the short period ends. A corporation that has dissolved must generally file by the 15th day of the 4th month after the date it dissolved.
The June 30 year-end exception, and what changes in 2026
The 2025 Form 1120 instructions say a corporation with a fiscal tax year ending June 30 must file by the 15th day of the 3rd month after its year ends, which is September 15. A short tax year ending anytime in June is treated as ending on June 30.
These corporations also get a longer extension. C corporations with tax years ending June 30 and beginning before January 1, 2026 are eligible for an automatic 7-month extension. For tax years beginning in 2026, the automatic extension period is 6 months.
Publication 509 (2026) gives the general 15th-day-of-the-4th-month rule and says corporations with a short tax year that began before January 1, 2026 and ends on June 30, 2026 must file by September 15, 2026. The draft 2027 calendar says the automatic 7-month extension for June 30 year ends has expired, and Form 7004 now gives 6 months.
Extending the deadline with Form 7004
Form 7004 requests an extension of time to file. The corporation generally must file it by the regular due date of the return. The automatic extension period is generally 6 months.
Form 7004 doesn't extend the time to pay. Any tax due must be paid in full by the regular due date, not including extensions, and interest is charged on late tax even when an extension is granted. A corporation with an extension isn't charged a late payment penalty if it paid at least 90% of the tax on its return by the regular due date and pays the rest by the extended date.
Certain domestic corporations that keep their books and records outside the United States and Puerto Rico get an automatic extension to file and pay until the 15th day of the 6th month after year end, without filing Form 7004.
Estimated tax deadlines during the year
A corporation must pay estimated tax in installments if it expects its total tax for the year, less credits, to be $500 or more. Installments are due by the 15th day of the 4th, 6th, 9th and 12th months of the tax year, moving to the next business day for weekends and holidays. For a calendar-year corporation that is April 15, June 15, September 15 and December 15.
Corporations must make all federal tax deposits, including estimated tax, by electronic funds transfer, using EFTPS or the corporation's IRS business tax account. EFTPS accepts same-day payments of $1 million or less submitted before 3:00 p.m. Eastern time on a business day.
The underpayment penalty, figured on Form 2220, generally applies when the tax is $500 or more and the corporation didn't pay on time at least the smaller of its current-year tax or its prior year's tax. Corporations figure their regular tax at 21% of taxable income.
Calendar-year dates for 2026 and 2027
For a 2026 calendar-year corporation, the draft 2027 IRS calendar lists Form 1120, or Form 7004 with a deposit of the estimated tax, on April 15, 2027, with the extended return due October 15, 2027.
Penalties for missing the corporate deadline
A corporation that doesn't file by the due date, including extensions, may be penalized 5% of the unpaid tax for each month or part of a month the return is late, up to 25%. For returns required to be filed in 2026 and more than 60 days late, the minimum penalty is the smaller of the tax due or $525. For returns required to be filed in 2027, Rev. Proc. 2025-32 sets that minimum at the lesser of $535 or 100% of the tax.
Paying late adds ½ of 1% of the unpaid tax for each month or part of a month, up to 25%. The late filing penalty isn't imposed if the corporation shows reasonable cause.
Corporations that file 10 or more returns of any type in a calendar year must e-file Form 1120.
Aldro prepares and files Form 1120, Form 7004 and the state corporate return for one flat yearly price that covers everything tax. Our team also works out the quarterly estimated tax amounts and dates.
Worked example
A calendar-year C corporation owes $40,000 of tax for 2025 and files Form 7004 on April 15, 2026, paying $36,000 that day. That is 90% of the tax, so if it files by October 15, 2026 and pays the last $4,000 with the return, the Form 7004 instructions say no late payment penalty applies, though interest runs on the $4,000 from April 15. If instead it filed nothing and paid nothing until three months after April 15, the late filing penalty alone could reach 5% x 3 months x $40,000 = $6,000, less any late payment penalty for the same months.
Common questions
When is Form 1120 due?
By the 15th day of the 4th month after the tax year ends, which is April 15 for a calendar-year corporation. Weekends and legal holidays move it to the next business day.
What is the extended corporate tax deadline?
Form 7004, filed by the regular due date, generally gives 6 more months, so October 15 for a calendar-year corporation. June 30 year ends beginning before January 1, 2026 get 7 months.
Does a corporation with no income still have to file by the deadline?
Yes. Unless exempt under section 501, every domestic corporation must file whether or not it has taxable income.
When are C corp estimated taxes due?
By the 15th day of the 4th, 6th, 9th and 12th months of the tax year, if the corporation expects $500 or more of tax. Payments must be made electronically.
Is the C corp deadline the same as the S corp deadline?
No. Form 1120 is due on the 15th day of the 4th month after year end. Form 1120-S is due a month earlier, on the 15th day of the 3rd month.
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Sources
- IRS: Instructions for Form 1120 · checked October 31, 2026
- IRS: Instructions for Form 7004 · checked October 31, 2026
- IRS: Publication 509, Tax calendars · checked October 31, 2026
- IRS: Publication 509 (2027), draft · checked October 31, 2026
- IRS: Publication 542, Corporations · checked October 31, 2026
- IRS: Rev. Proc. 2025-32 · checked October 31, 2026
This guide explains general rules from the sources listed. It isn’t tax advice for your situation.