The General Rule — File Regardless of Revenue

Every domestic corporation in existence during any part of the tax year must file a Form 1120 unless it is specifically exempt from filing or has elected to be taxed as an S corporation. This means a C corporation that was formed on December 30 and had no transactions must still file a return for that year. Corporations that are winding down, dormant, or in the process of dissolution also must continue filing until they are formally dissolved under state law and have distributed all assets.

The requirement applies whether the corporation is profitable or operating at a loss. Even a corporation with zero gross receipts must file to report its existence and any deductible expenses that create a net operating loss, which can be carried forward to offset future income.

Exempt Organizations and Special Cases

Certain corporations are exempt from filing Form 1120. Tax-exempt organizations file Form 990 instead. S corporations file Form 1120-S. Corporations within a consolidated group file as part of the parent corporation’s consolidated return on Form 1120. Insurance companies, regulated investment companies, and real estate investment trusts have their own specialized return forms. A corporation that has not yet begun business and has no income may be able to defer filing, but this exception is narrow and should not be assumed without professional guidance.

Due Dates and Extensions

Form 1120 is due on the 15th day of the fourth month after the end of the corporation’s tax year. For calendar-year corporations, this is April 15. An automatic six-month extension to October 15 is available by filing Form 7004, but the extension is for filing only — any estimated tax liability must still be paid by the original due date. Late filing carries a penalty of 5% of the unpaid tax per month, up to a maximum of 25%. The late payment penalty is 0.5% per month, also capped at 25%.

Estimated Tax Payments

C corporations with an expected tax liability of $500 or more must make quarterly estimated tax payments. These are due on the 15th day of the 4th, 6th, 9th, and 12th months of the tax year. Underpayment of estimated taxes can result in penalties calculated on the shortfall for each quarter. Large corporations — those with taxable income of $1 million or more in any of the three preceding years — face additional rules and cannot base their first-quarter estimate on the prior year’s tax liability for more than one quarter.