Form 1120 deadline: when a C corporation files its federal tax return

The IRS generally requires a corporation to file Form 1120 by the 15th day of the fourth month after the end of its tax year. A calendar-year C corporation therefore generally files by April 15. If the due date falls on a Saturday, Sunday, or legal holiday, it moves to the next business day.

Fiscal-year corporations calculate the deadline from their own year-end. The Form 1120 instructions also contain a special rule for corporations with a fiscal year ending June 30 and certain short tax years ending in June. Do not assume every C corporation has an April deadline.

A corporation can generally use Form 7004 to request an automatic extension of time to file. For most Form 1120 filers the extension is six months, subject to special rules. The extension changes the filing deadline; it does not postpone tax that was due with the original return.

The IRS generally requires a corporation to make estimated-tax installment payments if it expects its total tax for the year, after applicable credits, to be $500 or more. Installments are generally due on the 15th day of the fourth, sixth, ninth, and twelfth months of the corporation's tax year.

The filing deadline is the end of the process, not the start. A clean corporate return depends on reconciled books, payroll reports, fixed assets, equity activity, state-tax information, prior-year balances, and support for material expenses. Build the tax-preparation handoff into the monthly close so April does not become an annual reconstruction project.