https://www.irs.gov/businesses/small-businesses-self-employed/closing-a-business
When To File
Generally, a corporation must file its income tax return by the 15th day of the 4th month after the end of its tax year. A new corporation filing a short-period return must generally file by the 15th day of the 4th month after the short period ends. A corporation that has dissolved must generally file by the 15th day of the 4th month after the date it dissolved.
However, a corporation with a fiscal tax year ending June 30 must file by the 15th day of the 3rd month after the end of its tax year. A corporation with a short tax year ending anytime in June will be treated as if the short year ended on June 30, and must file by the 15th day of the 3rd month after the end of its tax year.
If the due date falls on a Saturday, Sunday, or legal holiday, the corporation can file on the next business day.
https://www.irs.gov/instructions/i1120
