C Corp Tax Return Due Date: Form 7004, Estimates, and Penalties

A C corporation’s federal tax return, Form 1120, is due by the 15th day of the fourth month after the end of its tax year. For a calendar-year C corp, that C corp tax return due date is April 15. If you need more time, filing Form 7004 by that same date pushes the filing deadline back six months, but the tax itself is still due on April 15.

April 15 for Calendar-Year C Corps

If your corporation’s tax year runs January 1 through December 31, Form 1120 and any remaining tax owed are due April 15 of the following year.¹ The return and the payment share the deadline. An extension of the return does not extend the payment.

When April 15 lands on a Saturday, Sunday, or legal holiday, including Emancipation Day in Washington, D.C., the deadline moves to the next business day.² Check the current year’s calendar rather than assuming April 15 is always in play.

Fiscal-Year C Corps

If your corporation uses a fiscal year, apply the same rule: the return is due the 15th day of the fourth month after your year-end.¹ A September 30 year-end means a January 15 deadline. A March 31 year-end means July 15. Weekend and holiday shifts apply the same way.

The June 30 Year-End Change

C corporations with a June 30 fiscal year-end have historically filed under an accelerated rule, with returns due September 15, the 15th day of the third month after year-end. That treatment still applies to any fiscal year that began before January 1, 2026, so a tax year running July 1, 2025 through June 30, 2026 is still due September 15, 2026.³

For tax years beginning on or after January 1, 2026, June 30 filers move onto the standard fourth-month rule. A year running July 1, 2026 through June 30, 2027 will be due October 15, 2027.⁴ The deadline shifts by a full month, so plan for it.

Extending the Deadline With Form 7004

Form 7004 gets you an automatic six-month extension to file. For a calendar-year filer, that moves the filing deadline from April 15 to October 15. Fiscal-year filers add six months to their normal due date. One holdover: a June 30 year-end corporation with a tax year that began before January 1, 2026 gets a seven-month extension, running from September 15 to April 15. That special extension ends with tax years beginning in 2026.⁴

Form 7004 has to be filed or postmarked by the original due date. You’ll estimate total tax for the year on the form, report what you’ve already paid, and pay the difference.

The Extension Does Not Extend Payment

This is where corporations get caught. Form 7004 buys time to prepare and file the return. It does not buy time to pay.⁵ The full estimated tax is still due on the original deadline.

There is a narrow cushion. You avoid the late-payment penalty if the amount paid by the original due date is at least 90 percent of the tax ultimately shown on the return, and the remaining balance is paid by the extended due date.⁴ Miss that 90 percent mark and interest and penalties run back to the original date. When estimating, err high.

Quarterly Estimated Tax Payments

A C corporation that expects to owe $500 or more in tax for the year has to pay in four quarterly installments rather than settle up at filing time.⁶ Each installment should be at least 25 percent of the required annual payment.

For calendar-year corporations, the four dates fall on:

April 15 (15th day of the 4th month)
June 15 (15th day of the 6th month)
September 15 (15th day of the 9th month)
December 15 (15th day of the 12th month)

Fiscal-year filers use the same pattern measured from their own year-end. A March 31 year-end, for instance, produces payment dates of July 15, September 15, December 15, and March 15.

The required annual payment can be based on the smaller of 100 percent of the current year’s tax or 100 percent of the prior year’s tax. The prior-year method only works if that prior year was a full 12 months and the corporation filed a return showing a liability. Large corporations (those with taxable income of $1 million or more in any of the three preceding years) can only use the prior-year figure for the first installment; every installment after that must be based on the current year, with any resulting shortfall from the first payment added to the second.⁷

Penalties for Filing or Paying Late

The IRS runs two separate penalties for missing the deadline, and they can stack.

Failure to File

If Form 1120 is not filed by the original or extended due date, the penalty is 5 percent of the unpaid tax for each month or partial month the return is late, capped at 25 percent.⁸ Because the penalty runs off unpaid tax, a corporation that has already paid its full bill will not face this penalty even if it files late, though it should still file quickly.

Returns more than 60 days late carry a minimum penalty of $525 or 100 percent of the unpaid tax, whichever is less, for returns with due dates after December 31, 2025.⁸

Failure to Pay

When the tax is not fully paid by the original due date, the penalty is 0.5 percent of the unpaid amount per month, also capped at 25 percent.⁵ Filing Form 7004 does not stop this penalty from running.

When both penalties apply in the same month, the IRS reduces the failure-to-file penalty by the failure-to-pay amount, producing a combined 5 percent per month rather than 5.5 percent.⁵ Interest accrues separately on any unpaid balance from the original due date and compounds daily.

Underpayment of Estimated Tax

Missing a quarterly installment or paying too little triggers a separate penalty on the shortfall for that period.⁷ It functions more like interest than a flat charge, running from the installment date until the payment date or the return due date, whichever comes first.

Final Return After Dissolution

A dissolving C corporation still owes a final Form 1120. The deadline is the 15th day of the fourth month after the date of dissolution, not the end of the corporation’s usual tax year.¹ A corporation dissolving on August 20 would file its final return by December 15, marked “Final Return” on the face of the form.

State Deadlines May Differ

Most states that tax corporate income tie their deadlines to the federal date, but not all. Some give an extra month; some do not automatically honor a federal extension. A timely federal Form 7004 does not guarantee extra time at the state level, so check with each state where the corporation files before assuming the federal calendar covers it.

1
Internal Revenue Service. Instructions for Form 1120 (2025)
2
Internal Revenue Service. Instructions for Form 1120 (2025)
3
Internal Revenue Service. Publication 509 (2026), Tax Calendars
4
Internal Revenue Service. Instructions for Form 7004 (Rev. December 2025)
5
Internal Revenue Service. Failure to Pay Penalty
6
Internal Revenue Service. Estimated Taxes
7
Office of the Law Revision Counsel. 26 USC 6655 – Failure by Corporation to Pay Estimated Income Tax
8
Internal Revenue Service. Failure to File Penalty