What is the deadline by which a c corporation must file it's tax return?

A C corporation must file its federal tax return using Form 1120 by the 15th day of the fourth month after the end of its tax year. For corporations that operate on a calendar year basis, this means the deadline is April 15. If the deadline falls on a weekend or holiday, it is extended to the next business day. Corporations can also request a six-month extension, pushing the deadline to October 15.