If you operate your business as an S corporation, the S corporation must file Form 1120S, U.S. Income Tax Return for an S Corporation, on an annual basis, to report income and deductions. Each shareholder must receive a copy of Schedule K-1 (part of Form 1120S), Shareholder's Share of Income, Credits, Deductions, etc., or a substitute K-1. For S corporations with a calendar tax year, the due date for the annual return and the Schedule K-1 is March 15.

The S 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 S corporation is filing for the six-month extension, it must deposit (at an authorized financial institution or a Federal Reserve Bank), what taxes it estimates it owes by the March 15 due date. An S corporation can use a Federal Tax Deposit (FTD) Coupon (IRS Form 8109) or it can deposit the amount due electronically. If an S corporation doesn't make a payment for the tax owed by the due date, it may be subject to interest and penalties on overdue taxes.

If your S 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 S corporation's tax year. A fiscal year S corporation is entitled to the same automatic six-month extension to file its return to which a calendar year S 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 S corporation's tax year. The actual return would then be due by the 15th day of the sixth month after the original return due date.

If you want your business to be treated as an S corporation, you must make an election by filing Form 2553, Election by a Small Business Corporation. For S corporations using a calendar tax year, this election must be filed by March 15. For S corporations using a fiscal tax year, the election must be filed by the 15th day of the third month of the first tax year to which the choice will apply or at any time during the preceding tax year.