Form 1120 Filing Deadlines and Extension Rules for C Corporations (2025-2026)

When Is Form 1120 Due?

Form 1120 is due on the 15th day of the 4th month after the end of the corporation's tax year. For calendar-year corporations (January 1 – December 31), the deadline is April 15.

There is one exception: corporations with a fiscal year ending June 30 must file by the 15th day of the 3rd month after year-end (September 15). This exception is being phased out for tax years beginning in 2026.

How to Request an Extension

File Form 7004 to request an automatic 6-month extension. For a calendar-year corporation, this extends the filing deadline from April 15 to October 15.

The extension only applies to filing — not to payment. If you owe taxes, the full amount is still due by the original deadline. Interest and penalties accrue on any unpaid balance from the original due date, even if you have a valid filing extension.

Estimated Tax Payments

C corporations generally must make quarterly estimated tax payments if they expect to owe $500 or more in tax for the year. Estimated payments are due on the 15th day of the 4th, 6th, 9th, and 12th months of the corporation's tax year.

For calendar-year corporations, the estimated payment dates are April 15, June 15, September 15, and December 15.

Penalties for Late Filing and Late Payment

The penalty for filing late is 5% of the unpaid tax for each month (or part of a month) the return is late, up to a maximum of 25%. The penalty for paying late is 0.5% of the unpaid tax per month, also up to 25%. Interest compounds daily on any unpaid balance from the original due date.