Do you know when your business tax returns are due?

 It depends on the type of legal entity of your business.

The instructions for the each type of form used will have the appropriate due date(s) noted:

 1.  The sole proprietor's Schedule C of income and expenses is attached to the Form 1040.  Therefore, the due date is the 15th day of the fourth month following the end of your tax year.  For most taxpayers who are on a calendar year, this is April 15. 

2.  A partnership generally must conform its tax year of the partners unless the partnership can establish a business purpose for having a different tax year.  The general definition states that you must file your return by the 15th day of the fourth month following the end of your tax year.

3.  A corporation may use either the calendar year, or a fiscal tax year.  The corporate tax return is due by the 15th day of the third month following the end of the tax year.

4.  An S corporation generally must use the calendar year, unless the entity can establish a business purpose for having a different tax year. The due date is the 15th day of the third month following the end of the tax year.

Source:  http://www.irs.gov