When Are Corporate Tax Returns Due With Extension?

A corporation that files Form 7004 on time gets an automatic six-month extension to file its income tax return in most cases. For a calendar-year C corporation, that pushes the deadline from April 15 to October 15. For a calendar-year S corporation, it moves from March 15 to September 15.¹ So when are corporate tax returns due with an extension? Six months after the original due date, with a few narrow exceptions covered below, and only if the corporation paid what it owed by that original date. An extension to file is not an extension to pay.²

Extended Due Date for C Corporations

C corporations file Form 1120. The original due date is the 15th day of the fourth month after the tax year ends.¹ For a calendar-year filer, that means April 15, and a timely Form 7004 moves the deadline to October 15.³

Fiscal-year C corporations use the same math. Add six months to the original due date. A corporation whose fiscal year ends March 31 has an original deadline of July 15 and an extended deadline of January 15 the following year.

The June 30 Fiscal Year Exception

C corporations with a fiscal year ending June 30 have historically received a seven-month extension instead of six. That longer extension applies only to tax years that began before January 1, 2026. For tax years beginning in 2026 and later, the extension reverts to the standard six months.⁴ If your fiscal year ends June 30, check which tax year the return covers before you calendar the deadline.

Extended Due Date for S Corporations

S corporations file Form 1120-S, and the original deadline is the 15th day of the third month after the tax year ends.⁵ For a calendar-year S corporation, that is March 15, or the next business day when March 15 falls on a weekend. The 2025 tax year return is due March 16, 2026, because March 15 lands on a Sunday.⁶ A six-month extension moves the deadline to September 15.

Fiscal-year S corporations add six months to their specific original due date. An S corporation with a fiscal year ending May 31 has an original deadline of August 15, so the extended deadline is February 15 of the following year.

Shareholder K-1s Move With the Extension

S corporations must furnish each shareholder a Schedule K-1 by the same date the corporate return is due. When the corporation extends, the K-1 deadline shifts with it, and shareholders do not receive their K-1s until the corporation actually files.⁶ Shareholders who need to file personal returns before the K-1 arrives may need their own extensions, or they can file with estimated figures and amend later. A penalty can apply to the S corporation for failing to furnish K-1s on time.

How to Request the Extension

Form 7004 is the only form needed. The extension is automatic: the IRS does not review or approve it. If the form is properly completed, filed by the original due date, and accompanied by payment of any expected tax due, the extension is granted.⁷

To fill it out, you need the corporation’s legal name, address, and EIN; the form code identifying the return being extended (12 for Form 1120, 25 for Form 1120-S); and your best estimate of the total tax the corporation owes for the year.⁸ If the corporation’s name changed since last year, use the old name on Form 7004 to avoid rejection. No signature is required.⁴

Most corporations file electronically through the IRS Modernized e-File system, which returns a digital confirmation of receipt.⁹ Paper filers send Form 7004 to the IRS Service Center for their region; the mailing address depends on the return type and the state where the principal office is located.⁴

For paper filings, the postmark date counts as the filing date. Certified mail with a return receipt gives you proof. The IRS also recognizes specific service tiers from DHL Express, FedEx, and UPS as satisfying the timely-mailing rule; standard ground shipping does not qualify.¹⁰

The Payment Is Still Due on the Original Date

This is the piece corporations most often get wrong. The six extra months apply to filing the return. The tax itself must be paid by the original, unextended due date.² The amount reported on Form 7004 should cover any remaining balance after accounting for quarterly estimated tax installments already made during the year.

Corporations generally avoid an underpayment penalty by paying, through quarterly installments, at least 100 percent of the prior year’s tax or at least 90 percent of the current year’s actual tax.¹¹ Any shortfall paid with Form 7004 stops additional failure-to-pay penalties from accruing on that amount, but it does not erase penalties or interest that already built up on underpaid quarterly installments.

What It Costs to Miss the Extended Deadline

Once the extended deadline passes without a filed return, the failure-to-file penalty kicks in. It is 5 percent of the unpaid tax for each month or partial month the return is late, capped at 25 percent.¹² If a return is more than 60 days late, a minimum penalty applies: $525 for returns due in 2026, or 100 percent of the unpaid tax, whichever is less.¹³

The failure-to-pay penalty runs separately. It is 0.5 percent of the unpaid tax per month, also capped at 25 percent.¹⁴ When both apply in the same month, the failure-to-file penalty is reduced by the failure-to-pay amount, so the combined charge for the first five months works out to 5 percent per month. After five months, only the failure-to-pay penalty keeps accruing.¹²

Interest runs on any unpaid tax from the original due date until the balance is paid. The IRS sets the rate quarterly; for the first quarter of 2026, corporate underpayments accrue at 7 percent per year, compounded daily.¹⁵

Asking for a Penalty Waiver

The IRS can waive failure-to-file and failure-to-pay penalties if the corporation shows the delay was due to reasonable cause and not willful neglect.¹⁴ Natural disasters that destroyed records, the serious illness or death of the person responsible for filing, and reasonable reliance on incorrect professional advice are common grounds. A clean filing history helps. Interest, however, cannot be waived, and it continues to accrue regardless of the reason for the delay.

State Extensions Follow Their Own Rules

A federal extension does not automatically extend state corporate returns. Some states honor the federal Form 7004 and require nothing else; others require a separate state extension form, and state deadlines do not always match the federal ones. Check your state’s department of revenue before assuming the federal extension covers you.

1
Internal Revenue Service. Publication 509 (2026), Tax Calendars
2
Internal Revenue Service. IRS Reminds Taxpayers an Extension to File Is Not an Extension to Pay Taxes
3
Office of the Law Revision Counsel. 26 U.S. Code 6081 – Extension of Time for Filing Returns
4
Internal Revenue Service. Instructions for Form 7004
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Internal Revenue Service. About Form 1120-S, U.S. Income Tax Return for an S Corporation
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Internal Revenue Service. Instructions for Form 1120-S
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Internal Revenue Service. Instructions for Form 7004
8
Internal Revenue Service. Form 7004
9
Internal Revenue Service. Modernized e-File (MeF) Status
10
Internal Revenue Service. Private Delivery Services (PDS)
11
Internal Revenue Service. Estimated Taxes
12
Internal Revenue Service. Failure to File Penalty
13
Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
14
Office of the Law Revision Counsel. 26 U.S. Code 6651 – Failure to File Tax Return or to Pay Tax
15
Internal Revenue Service. Quarterly Interest Rates