sectic Question 1 of 20. For calendar-year taxpayers, the normal filing due dates for business returns March 15 for Schedule C (Form 1040), and Forms 1120, 1120-s, and 1065. March 15 for Forms 1120, 1120-S, and 1065. Schedule C (Form 1040) is due March 15 for Forms 1120 and 1120-S. Schedule C (Form 1040) and Form 106 O March 15 for Forms 1065 and 1120-S. Schedule C (Form 1040) and Form 112 Mark for follow up