When Are Corporate Taxes Due? C Corp Tax Deadlines for 2026 and 2027

The corporation tax deadline comes from IRC 6072(a) and is restated in the 2025 Instructions for Form 1120. This guide answers when corporate taxes are due for calendar and fiscal years: the 1120 filing deadline, the June 30 exception that ends with tax years beginning in 2026, how weekends and holidays move a C corp tax deadline, the Form 7004 extension, the four corporate income tax deadline dates for estimated tax, and the late filing and late payment penalties, with worked numbers.

The Form 1120 due date rule

The statute sets two versions of the same deadline. Returns “made on the basis of the calendar year shall be filed on or before the 15th day of April,” and fiscal-year returns by “the 15th day of the fourth month following the close of the fiscal year” (IRC 6072(a)). The Form 1120 instructions add three details:

• A new corporation filing a short-period return files by the 15th day of the 4th month after the short period ends.
• A corporation that has dissolved generally files by the 15th day of the 4th month after the date it dissolved.
• The tax is due in full by the same date, not counting any extension. Corporations pay by electronic funds transfer, through EFTPS or the IRS business tax account.

For a calendar-year C corporation, the dates are:

Fiscal-year corporations: Form 1120 due dates by year-end month

Publication 509 lists calendar-year dates, and so does the business tax calendar, so a fiscal-year corporation counts from its own year end: 15th day of the 4th month, then 6 more months with a timely Form 7004 (Treas. Reg. 1.6081-3). For years ending in 2026:

The June 30 exception ends with 2026 tax years

When Congress moved the C corporation deadline from the 3rd month to the 4th in 2015, it kept the old date for one group: “In the case of any C corporation with a taxable year ending on June 30,” the change applies only to “taxable years beginning after December 31, 2025” (P.L. 114-41, section 2006(a)(3)). Until then, those corporations file by the 15th day of the 3rd month and get a 7-month extension instead of 6 (Treas. Reg. 1.6081-3(e)). A short year that ends any time in June is treated as ending June 30.

• Year from July 1, 2025 to June 30, 2026: the 2025 Form 1120 instructions apply the 3rd-month rule, so the return was due September 15, 2026, or is due April 15, 2027 with a 7-month extension.
• Year from July 1, 2026 to June 30, 2027: the general rule takes over. Form 1120 is due October 15, 2027, and Form 7004 adds 6 months.

The extended date lands in mid-April either way, since 3 months plus 7 equals 4 plus 6. What moves is the original due date, and with it the day the tax has to be paid: a month later than before.

Weekends, holidays and the next business day

When the last day falls on a Saturday, Sunday or legal holiday, IRC 7503 makes the next business day timely. Three details decide which day that is:

• “Legal holiday” means a legal holiday in the District of Columbia. D.C.’s list has the federal holidays plus Emancipation Day, April 16 (D.C. Code 1-612.02).
• A statewide holiday counts too, but only where the IRS office the return is filed with is located in that state.
• The rule applies to an extended due date as well, since the last day is figured by including any authorized extension.

In the fiscal-year table, that is why an April 30, 2026 year end is due Monday, August 17 (August 15 is a Saturday), and an October 31, 2026 year end is due Tuesday, February 16, 2027 (February 15 is Washington’s Birthday). The next September 30 year end shows the rule twice over: the return for the year ending September 30, 2027 falls due Tuesday, January 18, 2028, because January 15, 2028 is a Saturday and Monday, January 17 is Martin Luther King Jr. Day (computed).

Other corporate returns with their own deadlines

The S corporation rules, including Schedule K-1 timing and the per-shareholder penalty, are in the S corp tax deadline guide.

Extending Form 1120 with Form 7004

A corporation extends Form 1120 by filing Form 7004 with code 12 by the regular due date. The extension is automatic and lasts 6 months, 7 for a June 30 year that began before 2026. It covers filing only: the balance has to be deposited by the original date. A corporation is spared the late payment penalty for the extension period when its Form 7004 estimate, or what it paid by the due date, reached 90% of the final tax and it pays the rest by the extended date. Line-by-line instructions, the e-file exceptions and the mailing addresses are in the Form 7004 guide.

Corporate estimated tax: four more deadlines

A corporation that expects to owe $500 or more pays its current-year tax in four installments, on the 15th day of the 4th, 6th, 9th and 12th months of its tax year (IRC 6655(c), with 6655(i) substituting the matching months for a fiscal year). For 2026 calendar-year corporations those days are April 15, June 15, September 15 and December 15. The first installment for the new year shares April 15 with the prior year’s return, so extending the return does not delay it. How much each installment has to be, the safe harbors and the penalty on Form 2220 are covered in the guide to quarterly estimated taxes.

Example: a calendar-year and a fiscal-year corporation

Two hypothetical C corporations, one on the calendar year 2026 and one with a fiscal year from October 1, 2025 to September 30, 2026, face these dates:

The fiscal-year corporation’s next year, October 1, 2026 to September 30, 2027, has installments on January 15, March 15, June 15 and September 15, 2027, and a return due January 18, 2028.

Late filing and late payment penalties under IRC 6651

Two penalties apply to a C corporation, both measured as a share of the tax left unpaid after on-time payments and credits (IRC 6651(a) and (b)):

• Late filing: 5% of the unpaid tax for each month or part of a month the return is late, counted from the due date including any valid extension, up to 25%.
• Late payment: 0.5% of the unpaid tax for each month or part of a month after the original due date, up to 25%. After a notice of intent to levy, it becomes 1% a month once 10 days pass (IRC 6651(d)).
• Overlap: for any month both apply, the late filing penalty is reduced by the late payment penalty (IRC 6651(c)(1)), so the combined charge is 5% a month until the filing penalty tops out.
• Minimum: a return more than 60 days late owes at least the smaller of the tax due or $525 for returns required to be filed in 2026 (Rev. Proc. 2024-40), and $535 for returns required to be filed in 2027 (Rev. Proc. 2025-32).

Estimated tax shortfalls are a separate penalty under IRC 6655, figured on Form 2220, and IRC 6651 does not apply to them. Interest runs on unpaid tax from the due date even when an extension was granted, as the Form 1120 instructions note.

The flip side: because both penalties are percentages of unpaid tax, a corporation that paid everything by the due date owes no penalty under IRC 6651 even if the return is late. S corporations and partnerships work differently; their late filing penalty is charged per owner even when no tax is due.

Getting a penalty removed

Reasonable cause is the standing route: the regulations describe it as exercising “ordinary business care and prudence” and still being unable to file or pay on time (Treas. Reg. 301.6651-1(c)(1)). The Form 1120 instructions say to send the explanation after a penalty notice arrives, not with the return.

The IRS is also replacing its First Time Abate policy with Automatic Exemption from Penalty (IR-2026-83, July 8, 2026). It applies to eligible original returns beginning with tax year 2025, and Form 1120 is on the list. When a corporation timely filed the same return for the prior 3 years with no penalties other than for estimated tax, and meets the added tests for business filers, the late filing and late payment penalties are not assessed at all, and the IRS sends a notice saying so. The IRS set the switch to begin in summer 2026, so some 2025 returns may still draw a penalty notice; a corporation that qualifies can then ask for First Time Abate (IRS administrative penalty relief). Tax and interest are still owed either way.

Sources: 26 U.S.C. 6072, time for filing income tax returns; P.L. 114-41, section 2006 (return due dates and the June 30 rule); IRS, 2025 Instructions for Form 1120; IRS, 2025 Instructions for Form 1120-F; IRS, 2025 Instructions for Form 1120-C; IRS Publication 509 (2026), Tax Calendars; 26 CFR 1.6081-3, automatic extension for corporation income tax returns; 26 U.S.C. 7503, weekend and legal holiday rule; D.C. Code 1-612.02, legal public holidays; 26 U.S.C. 6655, corporate estimated tax; 26 U.S.C. 6651, failure to file tax return or to pay tax; 26 CFR 301.6651-1, failure to file or pay; IRS, Rev. Proc. 2024-40 (amounts for returns filed in 2026); IRS, Rev. Proc. 2025-32 (amounts for returns filed in 2027); IRS, IR-2026-83, automatic penalty relief (July 8, 2026); IRS, Administrative penalty relief (reviewed July 14, 2026). Rules, dates and amounts checked against these sources in September 2026. This is general information, not tax advice for your situation. Tax services are provided by licensed tax professionals under a separate engagement agreement. BEG does not provide tax advice.