Form 1040. This form is due on the 15th day of the 4th month after the end of your tax year. Form 4868 is used to request an extension of time to file Form 1040.
Estimated tax payments (Form 1040-ES). Payments are due on the 15th day of the 4th, 6th, and 9th months of your tax year and on the 15th day of the 1st month after your tax year ends.
Partnerships Form 1065. This form is due on the 15th day of the 3rd month after the end of the partnership's tax year. Provide each partner with a copy of Schedule K-1 (Form 1065) or a substitute Schedule K-1. Same deadline now for S-Corps form 1120S.
Corporations Form 1120 (or Form 7004). These forms are due on the 15th day of the 4th month after the end of the corporation's tax year.