If you operate your business as a corporation, the corporation must file Form 1120, U.S. Corporation Income Tax Return (or if it qualifies, Form 1120-A, U.S. Corporation Short-Form Income Tax Return), on an annual basis, to report income and deductions. For corporations with a calendar tax year, the due date for the annual return is March 15.

The corporation may apply for an automatic six-month extension to file its annual return by filing Form 7004, Application for Automatic Extension of Time To File Corporation Income Tax Return, by March 15. The return would then be due on September 15. If your corporation is filing for the six-month extension, it must deposit (at an authorized financial institution or a Federal Reserve Bank), whatever taxes it estimates it owes by the March 15 due date. A corporation can use a Federal Tax Deposit (FTD) Coupon (IRS Form 8109) or it can deposit the amount due electronically. If a corporation doesn't make a payment of the tax owed by the due date, it may be subject to interest and penalties on overdue taxes.

If your corporation uses a fiscal year rather than a calendar year, the annual corporate return must be filed by the 15th day of the third month after the end of the corporation's tax year. A fiscal year corporation is entitled to the same automatic six-month extension to file its return to which a calendar year corporation is entitled. The due date for the filing of the extension is the original due date of the return - the 15th day of the third month after the end of the corporation's tax year. The actual corporate return would then be due by the 15th day of the sixth month after the original return due date.