Tax filing deadlines depend on your business structure.
Returns for sole proprietors and calendar-year C corporations are generally due on April 15. Returns for partnerships, multi-member LLCs and S corporations are due on March 15.
Business owners are also generally required to make quarterly estimated tax payments. Those payments are due on April 15, June 15, Sept. 15 and Jan. 15 of the following tax year.
If any tax deadline falls on a weekend or holiday, the due date shifts to the following business day. There are also special rules for fiscal year taxpayers, which you can find in Chapter 2 of IRS Publication 505.