Who Files Form 1065 or 1120-S by March 15, 2027
17 October 2026 · Educational information · No affiliate links · 3 min read
General information, not tax, legal or financial advice. We are not the IRS. Check IRS.gov or a qualified tax professional. Sources read on October 17, 2026. Dates after 2026 are expected and amounts for 2026 returns may change. This page contains no affiliate links.
Short answer: a domestic partnership files Form 1065, and an S corporation files Form 1120-S. Both are due the 15th day of the 3rd month after the tax year ends. For calendar-year entities that is March 15, 2027, a Monday, so no weekend shift is expected.
Form 1065 (partnerships and multi-member LLCs taxed as partnerships)
- The 2025 instructions say that, except as provided there, every domestic partnership must file Form 1065 unless it neither receives income nor incurs any expenditure treated as a deduction or credit for federal income tax purposes.
- An LLC classified as a partnership for federal income tax purposes has the same filing requirements as a domestic partnership.
- A married couple that jointly owns and runs an unincorporated business is generally a partnership and files Form 1065, unless they qualify for and make the qualified joint venture (QJV) election (IRS Form 1065 instructions); a business held in the name of a state-law entity such as an LLC does not qualify for the QJV election.
- A single-member LLC is a different case: the instructions describe it as a possible disregarded entity for federal income tax purposes. Whether yours files a 1065 depends on its classification. See LLC tax classification and which return applies.
Form 1120-S (S corporations)
A corporation or other entity must file Form 1120-S if (a) it elected to be an S corporation by filing Form 2553, (b) the IRS accepted the election, and (c) the election remains in effect. See the Form 2553 checklist.
Due date rule
- Form 1065: "by the 15th day of the 3rd month following the date its tax year ended"; for calendar-year partnerships, March 15 (IRS instructions).
- Form 1120-S: the 15th day of the 3rd month after the end of the tax year. A corporation that has dissolved must generally file by the 15th day of the 3rd month after it dissolved.
- If the due date falls on a Saturday, Sunday, or legal holiday in the District of Columbia or the state in which the return is filed, a return filed on the next day that is not a Saturday, Sunday, or legal holiday is treated as timely (Form 1065 instructions). The 2025 instructions applied this to 2026 (March 16, 2026, because March 15, 2026 was a Sunday). March 15, 2027 is a Monday.
- Fiscal-year entities: count the 3rd month from their own year-end.
Quick table (expected for calendar-year entities)
| Entity | Return | Expected due date for 2026 | Extension (Form 7004) |
|---|---|---|---|
| Partnership / LLC taxed as partnership | 1065 | March 15, 2027 | Expected September 15, 2027 |
| S corporation | 1120-S | March 15, 2027 | Expected September 15, 2027 |
FAQ
Does Form 7004 push back the payment? No; see the Form 7004 guide.
When do partners get their K-1? See Schedule K-1 due dates.
Is the state return due the same day? Not necessarily; this page does not cover state deadlines.
What we could not verify
- State annual reports, franchise taxes and state returns: due dates vary by state and were not checked.
- Whether a specific entity qualifies for one of the exceptions in the 1065 instructions (foreign partnerships, certain others): only the general rule was read.
- 2026-year instructions for both forms (not yet published; dates are expected from the rule, not from a 2027 notice).
Sources (official)
- IRS, Instructions for Form 1065 (2025) (read October 17, 2026)
- IRS, Instructions for Form 1120-S (2025) (read October 17, 2026)