S corp filingThe ordinary company date.

March 15 is the ordinary date for a calendar-year Form 1120-S. September 15 is the ordinary extended date. Both days come from the federal calendar, so a shop on either coast is looking at the same two days. We do not reprint them as a local custom.

March 15, 2026 fell on a Sunday. September 15, 2026 fell on a Tuesday. March 15, 2027 falls on a Monday. September 15, 2027 falls on a Wednesday. We print the weekday so you can see the calendar. We do not teach that a weekend date legally moves. If you want to know what your own file should do when a date lands on a Sunday, bring the acknowledgment you have and we will say which paper it is.

An extension acknowledgment is a different paper. It does not fill the three proofs. It does not stand in for the receipt of Form 1120-S, it does not put a K-1 in an owner's hands, and it does not make wage forms match the register.

We still want the work started in the fall, while the year is open. Waiting until the week of the ordinary date is how receipts stay in a drawer and wage lines stay mislabeled. The calendar is a backstop. The close is the work.

We will not print one due date for every company. A fiscal year has its own ordinary date. A company that is not filing Form 1120-S is not on this calendar. The acceptance letter is what tells us this calendar applies.

We will not describe the personal return's date on this page. The company date is early so the K-1 can leave in time. That is the whole lesson.

If your company uses a fiscal year, bring the year end with the letter. We will not force March 15 onto a year that does not end in December. The weekday notes above are only for the ordinary calendar-year dates.