Each US corporation that isn’t tax-exempt files a federal income tax return with the IRS each year, even when it has no taxable income. It can owe state tax too, such as California’s franchise tax when it does business there.
This page explains general rules, not legal or tax advice for your company. Rules change, and they depend on where your company is registered and where your people work. Before you act, check with your own lawyer, accountant or tax advisor.
Who files and when
The return is Form 1120, unless the IRS requires, or the corporation elects, a special return. An S corporation, for one, files Form 1120-S, due by the 15th day of the 3rd month after its tax year ends. A corporation that isn’t an S corporation can use the calendar year or a fiscal year as its tax year. Its Form 1120 is due by the 15th day of the 4th month after the tax year ends: April 15 for a calendar year.- A corporation whose tax year ends June 30 and began before January 1, 2026 files by the 15th day of the 3rd month after it ends. A short tax year that ends in June, such as a new or dissolved corporation’s, counts as ending June 30.
- 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 files by the 15th day of the 4th month after the date it dissolved.
- When the due date falls on a Saturday, Sunday or legal holiday, the corporation can file on the next business day.
Extend the time to file
Form 7004 gives a corporation an automatic extension of time to file Form 1120. The corporation files it by the return’s due date, and a calendar-year corporation then has until October 15 to file. A corporation whose tax year ends June 30 and began before January 1, 2026 gets 7 months instead. Form 7004 doesn’t extend the time to pay. The tax is still due by the original date, and the IRS charges interest on tax paid late even when it granted an extension.Estimated tax
A corporation that expects its federal tax for the year, less credits, to be $500 or more pays estimated tax in installments. They’re due by the 15th day of the 4th, 6th, 9th and 12th months of its tax year, and it pays them by electronic funds transfer. An installment not paid when due may bring an underpayment penalty.Late filing and late payment
A corporation that doesn’t file by the due date, extensions included, may be penalized for each month or part of a month the return is late. The penalty isn’t imposed when the corporation can show reasonable cause. Tax paid late may draw a penalty for each month or part of a month it stays unpaid. The IRS’s Instructions for Form 1120 give each penalty’s rate.State corporate taxes
The IRS’s State government websites page links each state’s site, with its information on doing business and taxes there.Delaware
The Delaware Division of Revenue says a corporation incorporated in Delaware that doesn’t do business there isn’t subject to Delaware’s corporate income tax. The corporation still pays Delaware’s franchise tax and files its annual franchise tax report by March 1 (see File your Delaware franchise tax).California
A corporation formed in another state is subject to California’s franchise tax once it completes with the California Secretary of State. It’s also subject to the tax when it does business in California without qualifying. Each corporation that’s incorporated, qualified or doing business in California must pay California’s minimum franchise tax. The Franchise Tax Board publishes the amount. A corporation newly incorporated or qualified in California doesn’t pay the minimum in its first taxable year. California counts a corporation as doing business there if it:- engages in any transaction for financial gain in California
- is organized or commercially domiciled in California
- has California sales, property or payroll above the amount the Franchise Tax Board lists for each year on Doing business in California, or above 25% of its total sales, property or payroll