When To File

Generally, an S corporation must file Form 1120-S by the 15 day of the 3rd month after the end of its tax year. For calendar year corporations, the due date is March 16, 2026 (March 15th falls on Sunday). A corporation that has dissolved must generally file by the 15th day of the 3rd month after the date it dissolved.

If the due date falls on a Saturday, Sunday, or legal holiday, the corporation can file on the next day that isn’t a Saturday, Sunday, or legal holiday.

If the S corporation election was terminated (other than by reason of making a section 336(e) election, discussed immediately below) during the tax year and the corporation reverts to a C corporation, file Form 1120-S for the S corporation’s short year by the due date (including extensions) of the C corporation’s short year return.

Caution: If the S corporation is making a section 336(e) election with respect to a qualified stock disposition, in most cases the S corporation is deemed to liquidate and its tax year ends and its S corporation election terminates on the date of the qualified stock disposition. See Regulations section 1.336-2(b)(1)(iii)(A). The S corporation generally must file Form 1120-S (with the section 336(e) election statement attached) for its tax year ending on the date of the qualified stock disposition by the 15th day of the 3rd month after the date of the qualified stock disposition. See Regulations section 1.336-2(h)(2)(iii) for the requirements for an S corporation to make a section 336(e) election.

Private Delivery Services Corporations can use certain private delivery services (PDS) designated by the IRS to meet the “timely mailing as timely filing” rule for tax returns. Go to IRS.gov/PDS for the current list of designated services.

The PDS can tell you how to get written proof of the mailing date.

For the IRS mailing address to use if you are using a PDS, go to IRS.gov/PDSStreetAddresses .

Caution: Private delivery services can’t deliver items to P.O. boxes. You must use the U.S. Postal Service to mail any item to an IRS P.O. box address.

Extension of Time To File File Form 7004, Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns, to ask for an extension of time to file. Generally, the corporation must file Form 7004 by the regular due date of the return. See the Instructions for Form 7004.

• Sign the return in the space provided for the preparer’s signature,