Businesses must file annual federal income tax returns by a set due date. For partnerships and S corporations on a calendar year, the deadline is March 15 (e.g., March 15, 2021, for the 2020 return); for calendar-year C corporations and sole proprietors, the deadline is April 15 (e.g., April 15, 2021, for the 2020 return). Businesses that can’t meet the deadline may obtain a filing extension. There’s much confusion about the rules impacting filing extensions.
