A C corporation files Form 1120 and pays any tax due by the 15th day of the 4th month after its tax year ends: April 15 for a calendar year. Form 7004 gives an automatic 6-month extension of time to file, but the tax is still due by the original date.
Check the date against your own records.
Fiscal years
Count from the end of your tax year. A corporation with a September 30 year end files by January 15, and one with a March 31 year end by July 15.
Estimated tax
A corporation that expects to owe tax pays it in installments on the 15th day of the 4th, 6th, 9th and 12th months of the tax year: April 15, June 15, September 15 and December 15 for a calendar year.
Weekends and holidays
If a due date falls on a Saturday, Sunday or legal holiday, it moves to the next business day.
Also on the calendar
Delaware corporations file their annual report and franchise tax by March 1. A foreign-owned single-member LLC files a pro forma Form 1120 with Form 5472 on the same date as Form 1120.
Get reminded before it's due
Regmindr tracks this alongside the rest of your compliance calendar, and emails your team before each deadline. Set it up from your year end in about two minutes.
Sources
This page is a summary, not legal or regulatory advice. The rules in the sources above take precedence.