The due date for a short year tax return is the 15th day of a specific month after the short period ends, and which month depends on the entity. C-corporations, estates, and trusts file by the 15th day of the fourth month. S-corporations, partnerships, and multi-member LLCs taxed as partnerships file one month earlier, on the 15th day of the third month. The same deadlines apply whether the short year came from a new formation, a dissolution, or a change in accounting period.
Due Dates by Entity Type
The calculation is the same regardless of why the short year exists. Count forward from the last day of the short period to the required month, then land on the 15th.
C-Corporations (Form 1120)
Form 1120 for a short period is due on the 15th day of the fourth month after the short period ends.1Internal Revenue Service. Instructions for Form 1120 A short year ending September 30 produces a January 15 deadline. A corporation that dissolves on June 15 owes its final return by October 15.
S-Corporations (Form 1120-S) and Partnerships (Form 1065)
S-corporations and partnerships file on the 15th day of the third month after the short period ends, one month earlier than C-corporations.2Internal Revenue Service. Instructions for Form 1120-S (2025)3Internal Revenue Service. Instructions for Form 1065 (2025) – Section: When To File A partnership with a short year closing September 30 must file by December 15. An S-corporation that dissolves March 20 owes its final return by June 15.
Multi-member LLCs that have not elected corporate treatment follow the partnership schedule.3Internal Revenue Service. Instructions for Form 1065 (2025) – Section: When To File
Estates and Trusts (Form 1041)
Form 1041 is due on the 15th day of the fourth month after the short period ends, the same schedule as a C-corporation.4Internal Revenue Service. Forms 1041 and 1041-A: When to File An estate whose short year ends June 30 must file by October 15.
Deceased Individuals (Form 1040)
The final individual return for someone who died mid-year covers January 1 through the date of death. Even though the reporting period is short, the return is due on the normal April 15 deadline for the year of death.5Internal Revenue Service. Filing a Final Federal Tax Return for Someone Who Has Died The surviving spouse or personal representative signs and files it. Any estate that comes into existence has a separate Form 1041 filing obligation.
Weekends and Holidays
If the calculated date falls on a Saturday, Sunday, or legal holiday, the deadline moves to the next business day.6Internal Revenue Service. When to File
Filling Out the Return for a Short Period
A short-period return uses the same form as a full year. C-corporations file Form 1120, S-corporations file Form 1120-S, partnerships and multi-member LLCs file Form 1065, and estates and trusts file Form 1041.1Internal Revenue Service. Instructions for Form 11207Internal Revenue Service. Instructions for Form 1065 (2025) Enter the actual short period in the “Tax Year Beginning” and “Tax Year Ending” boxes at the top of the return rather than a standard 12-month span. If the filing closes the entity, check the final return box.
Extending a Short Year Deadline
Form 7004 grants an automatic extension for business returns, and it works the same way for a short period as for a full year. It must be filed on or before the original short-period due date.8Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns
The length of the extension depends on the entity:
- Corporations, S-corporations, and partnerships get six months from the original deadline.
- Estates and trusts filing Form 1041 get five and a half months.
These periods come from the Form 7004 instructions.9Internal Revenue Service. Instructions for Form 7004 (12/2025) A C-corporation whose short year return was originally due November 15 would have until May 15 of the following year. An S-corporation with a December 15 deadline would push to June 15.
An extension buys time to file, not time to pay. Any estimated tax owed is still due on the original date. Missing that payment triggers interest and the failure-to-pay penalty even if the return itself arrives inside the extension window.
Form 7004 can be e-filed or mailed. It requires the entity’s EIN and the exact tax year ending date of the short period.
What Missing the Date Costs
Short-year deadlines land on unusual dates, and the routine March or April muscle memory doesn’t help. The penalties for filing late are the same as they would be for a full-year return.
Failure to File
For a C-corporation, the failure-to-file penalty is 5% of the unpaid tax for each month or partial month the return is late, capped at 25%. If the return is more than 60 days late, the minimum penalty is the smaller of $525 or 100% of the unpaid tax.10Internal Revenue Service. Failure to File Penalty
Partnerships and S-corporations are penalized per owner. The charge is $255 per partner or shareholder for each month the return is late, up to 12 months. A 10-member partnership that files four months late owes $10,200 ($255 × 10 × 4).10Internal Revenue Service. Failure to File Penalty The per-owner math is why a missed short-year date can be more expensive for a pass-through than the tax liability alone would suggest.
Failure to Pay
Unpaid tax draws a separate 0.5% penalty per month, up to 25%. When failure-to-file and failure-to-pay apply in the same month, the failure-to-file rate is reduced to 4.5%, keeping the combined charge at 5% per month.11Internal Revenue Service. Failure to Pay Penalty
Interest
Interest runs on unpaid tax from the original due date and compounds daily. For the quarter beginning April 1, 2026, the underpayment rate is 6% for most taxpayers and 8% for large corporate underpayments.12Internal Revenue Service. Internal Revenue Bulletin: 2026-08 Rates are set quarterly, so the rate when your short-period return is due may differ from the one above.