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C Corporation Filing Requirements

C-Corporation Tax Filing Requirements | Z-Tax & Accounting

Who Must File a C-Corporation Tax Return

Every domestic C-Corporation that exists during any part of a tax year — including those with no income, no business activity, or even in bankruptcy — must file a federal income tax return.

C-Corporations report their income, deductions, and taxes using IRS Form 1120 (U.S. Corporation Income Tax Return).

Other types of corporations may have different filing requirements:

Foreign corporations must file Form 1120-F.
Tax-exempt corporations file Form 990 instead of Form 1120.

Failing to file the required return can result in IRS penalties and interest, even if the corporation had no taxable income.

C-Corporation Tax Filing Deadlines

For most corporations, Form 1120 must be filed by the 15th day of the fourth month after the end of the corporation’s tax year.

Calendar Year Corporations (ending December 31): File by April 15 of the following year.
Fiscal Year Corporations (ending June 30): File by September 15. This rule applies until at least December 2025 (subject to extension).

Extended Due Dates

If a corporation needs more time to file, it can request an automatic six-month extension.

For calendar year corporations, the extended filing deadline is October 15.

Keep in mind, an extension gives more time to file, but not more time to pay any taxes owed.

Do Inactive or Loss Corporations Need to File?

Yes. A C-Corporation must continue to file Form 1120 every year, even if it had no business activity or profits.
The only time filing is no longer required is after the corporation has been formally dissolved through proper state and IRS procedures.