Exception:

for tax years beginning before 2026, if the taxable year ends on June 30 (or if the return is for a short period that ends on any day in June), the due date is the 15th day of the 3rd month following the close of the tax year.

foreign C Corporation has an office or place of business within the U.S.

for tax years ending prior to January 1, 2016, the due date is the 15th day of the 3rd month following the tax year.

foreign corporation does not have an office or place of business within the U.S.

must file on or before the 15th day of the 6th month following the tax year.