Calendar-year C corporations must file Form 1120 and pay any tax owed by April 15 of the following year. For the 2026 tax year, that date is April 15, 2027. Corporations on a fiscal year follow a different clock, because their deadline is the 15th day of the fourth month after the tax year ends.
This guide covers original due dates, extension dates, quarterly estimated payments, S corporation and partnership deadlines, and what happens when a date slips. The dates come from IRS instructions and the Internal Revenue Code, and they apply to federal returns only.
Federal Corporate Tax Due Dates at a Glance
| Entity | Form | Original Due Date (Tax Year 2026, Calendar Year) | Extended Due Date |
| C corporation | 1120 | April 15, 2027 | October 15, 2027 |
| S corporation | 1120-S | March 15, 2027 | September 15, 2027 |
| Partnership or multi-member LLC taxed as one | 1065 | March 15, 2027 | September 15, 2027 |
| Tax-exempt organization | 990 | May 17, 2027 | November 15, 2027 |
If a due date lands on a weekend or federal holiday, the deadline moves to the next business day. March 15, 2026 fell on a Sunday, for instance, so S corporation returns for tax year 2025 were due March 16, 2026. None of the main 2027 dates in the table fall on a weekend, but May 15, 2027 does, which is why the Form 990 date shows May 17.
One date is close right now. Calendar-year C corporations that filed Form 7004 for tax year 2025 have until Thursday, October 15, 2026, to file their return.
Who Follows the Form 1120 Deadline
The Form 1120 timeline applies to any entity the IRS taxes as a C corporation. That includes corporations that never elected S status and LLCs that filed Form 8832 to be taxed as corporations. An S corporation election through Form 2553 moves the entity to the earlier Form 1120-S date instead.
Foreign corporations with U.S. income file Form 1120-F, which has its own due date rules based on whether the company has a U.S. office. Tax-exempt nonprofits file Form 990 in most cases. When you are unsure which return applies, the entity’s tax classification decides, not its legal name.
When Form 1120 Is Due for C Corporations
A C corporation pays its own income tax at a flat 21% federal rate under section 11 of the Internal Revenue Code. It reports that tax on Form 1120, and the return is due on the 15th day of the fourth month after the tax year ends, as set by section 6072 of the Code.
For a corporation on the calendar year, that means April 15. Tax year 2025 returns were due April 15, 2026, and tax year 2026 returns are due April 15, 2027.
The payment date matters as much as the filing date. Even with an extension, the tax owed is due by the original date, and interest runs from that day on any unpaid balance.
Fiscal-Year Corporations Count From the Year-End Month
A fiscal year is any 12-month period that ends on the last day of a month other than December. The due date still lands on the 15th, just in a different month. Take the month the year ends, count four months forward, and use the 15th of that month.
Two examples show how this works. A corporation with a September 30, 2026 year-end owes its return on January 15, 2027, and can extend to July 15, 2027. One with a January 31, 2027 year-end counts to May 15, 2027, which is a Saturday, so the return is due Monday, May 17, 2027.
Corporations with a June 30 year-end had an earlier special due date under prior law. That rule ends for tax years beginning after December 31, 2025, so check the IRS Form 7004 due date chart before assuming a date.
Estimated Tax Payments Are Due Four Times a Year
Corporations do not wait for the return to pay. A corporation that expects to owe $500 or more for the year must make installment payments on the 15th day of the fourth, sixth, ninth, and twelfth months of its tax year, according to the IRS instructions for Form 1120-W.
For a calendar-year corporation, the 2026 installments fall on April 15, June 15, September 15, and December 15, 2026. The next one is Tuesday, December 15, 2026. In 2027, the pattern repeats, ending with Wednesday, December 15, 2027.
Each installment is generally 25% of the required annual payment. Large corporations, defined as those with taxable income of $1 million or more in any of the three prior years, face a stricter rule. They can use the prior year’s tax to size only the first installment, so later payments have to track current-year income.
Underpaying triggers a penalty calculated on Form 2220. Corporations also must pay electronically, usually through the Electronic Federal Tax Payment System (EFTPS).
How Form 7004 Extends the Filing Deadline
Form 7004 gives most C corporations an automatic six-month extension to file Form 1120. For a calendar-year corporation, the extended deadline is October 15, which is October 15, 2027, for tax year 2026. The IRS grants it automatically if you file the form by the original due date, make a proper estimate of the tax, and pay what is due, per the Instructions for Form 7004.
An extension never moves the payment date. Those same instructions state that Form 7004 does not extend the time to pay tax. They also describe late-payment penalty relief for a corporation whose tax paid by the regular due date is at least 90% of the tax shown on the return, provided the balance is paid by the extended due date.
File electronically when you can, since most returns qualify. One form covers one return, so a corporation requesting extensions for more than one return needs a separate Form 7004 for each. Tax-exempt organizations use Form 8868 instead, and mixing up the forms produces no valid extension.
S Corporation and Partnership Deadlines Come First
S corporations and partnerships generally pay no federal income tax at the entity level, so their timeline works differently. Form 1120-S and Form 1065 are due on the 15th day of the third month after year-end, which is March 15 for calendar-year entities. The earlier date exists because owners need their Schedule K-1 before they can finish personal returns.
A timely Form 7004 extends both returns by six months, to September 15 for calendar-year filers. An owner still waiting on a K-1 often has to extend a personal return as well.
Entity-level penalties apply per owner. The IRS charges a monthly amount for each shareholder or partner when an S corporation or partnership return is late, for up to 12 months, and the dollar figure is adjusted each year. Multi-member LLCs taxed as partnerships follow the Form 1065 timeline, not Form 1120-S, unless they elected corporate treatment.
State Deadlines Do Not Always Match the Federal Calendar
Federal dates cover only the IRS. Most states with a corporate income tax set their own due dates and extension rules. Some follow the federal extension automatically, while others require a separate form or payment, and states also set their own estimated payment dates.
Franchise and annual report taxes run on separate schedules too. The Texas Comptroller sets May 15 for franchise tax reports, and the Delaware Division of Corporations sets March 1 for the annual report and franchise tax. Check your state revenue department’s site before relying on the federal date.
What Happens When You Miss a Corporate Tax Deadline
Late filing costs more than late payment. The IRS failure-to-file penalty is 5% of the unpaid tax for each month or part of a month the return is late, capped at 25%. The failure-to-pay penalty is 0.5% per month, also capped at 25%, and interest accrues on top of both, under section 6651 of the Internal Revenue Code and IRS penalty guidance.
When both penalties apply in the same month, the filing penalty is reduced by the payment penalty, so the combined rate is 5% for that month. That is the main reason to file an extension even when you cannot pay in full. It stops the larger penalty from growing.
Returns more than 60 days late also face a minimum penalty, which is the lesser of a fixed dollar amount the IRS adjusts yearly or 100% of the tax due. Relief exists through reasonable cause and, for some filers with a clean record, first-time penalty abatement. Interest rates reset quarterly, so confirm the current rate on IRS.gov before calculating a payoff.
Special Cases That Change the Due Date
Newly Formed Corporations
A new corporation’s first tax year starts on the day it begins business, which is often mid-year. Its first return is due on the 15th day of the fourth month after that short year ends. If the owners choose a fiscal year at formation, the same counting rule applies.
Corporations That Dissolve
A corporation that dissolves must file a final Form 1120 by the 15th day of the fourth month after the dissolution date. It also files Form 966 within 30 days after adopting a plan to dissolve. State dissolution filings run on their own timeline, so confirm both with a tax professional.
A Practical Routine for Hitting Every Deadline
Work backward from the due date, not forward from the year-end. Start with the filing deadline, subtract the time your accountant needs, then subtract the time your bookkeeping needs to close the books. A calendar-year corporation aiming to file by April 15 usually wants closed books by late February, so the preparer has weeks rather than days.
Decide on an extension early. If the books are not final by mid-March, filing Form 7004 costs little and removes the pressure to rush. Send a payment estimate with it.
Put the four estimated payment dates on the calendar as soon as the return is filed. Schedule them in EFTPS so a missed reminder does not become an underpayment penalty.
Keep a one-page tracker with the federal date, the state date, and the extended date for each entity you own. An owner with both a C corporation and an S corporation runs two calendars, and the March 15 date arrives first.
