When Is the S Corp Tax Return Due? Form 1120-S Deadlines for 2026 and 2027

The S corp tax deadline is earlier than the C corporation date and the individual April date, and missing it is charged per shareholder. This guide answers when an S corp tax return is due under the 2025 Instructions for Form 1120-S: the 1120-S deadline for 2025 and 2026 returns, the S corp tax due date for any tax the corporation itself owes, when Schedules K-1 reach shareholders and why that date drives their own returns, the Form 7004 extension, and how the IRC 6699 penalty adds up, with an illustration. If you are still deciding on the structure, start with what an S corporation is.

Form 1120-S due dates

The Code puts S corporations with partnerships on the March schedule: returns “made on the basis of the calendar year shall be filed on or before the 15th day of March,” and fiscal-year returns by the 15th day of the third month after the year closes (IRC 6072(b)). The Form 1120-S instructions apply it to 2025 returns: “For calendar year corporations, the due date is March 16, 2026 (March 15th falls on Sunday).”

Most S corporations use the calendar year. The Form 2553 instructions allow a fiscal year only in listed cases: a natural business year, an ownership tax year, a year elected under section 444, a 52-53-week year tied to one of those, or a year with an established business purpose. A fiscal-year S corporation files by the 15th day of the 3rd month after its own year end, so a September 30 year end means a December 15 due date. The business tax calendar lists every calendar-year date.

Special cases that change the date

• The first year. The instructions say not to file Form 1120-S for any tax year before the year the election takes effect, and that year turns on when Form 2553 was filed.
• A mid-year termination. If the S election ends during the year and the corporation becomes a C corporation, the Form 1120-S for the S short year is due by the due date, including extensions, of the C short-year return. That return follows the C corporation deadline of the 15th day of the 4th month.
• Dissolution. A dissolved S corporation generally files by the 15th day of the 3rd month after the date it dissolved.
• A section 336(e) election. When a qualified stock disposition ends the tax year, the return with the election statement is generally due by the 15th day of the 3rd month after the disposition date.
• Weekends and holidays. A due date on a Saturday, Sunday or legal holiday moves to the next day that is none of those, which is why 2026 had March 16.

Schedule K-1s go out on the same day

Every S corporation furnishes each person who was a shareholder at any time during the year a copy of their share of the return’s items “on or before the day on which the return for such taxable year was filed” (IRC 6037(b)). The instructions put it as the day Form 1120-S is required to be filed, and Publication 509 tells an extended S corporation to provide the K-1s by September 15. So the K-1s leave with the return: March 16, 2026 for an unextended 2025 return, or the day an extended return is filed, no later than September 15, 2026.

• Schedule K-3. A corporation with items of international tax relevance may owe shareholders a Schedule K-3 on the same timeline. One that meets the domestic filing exception must notify shareholders, on or with the K-1 or separately, before it files Form 1120-S.
• Late or wrong K-1s. Each K-1 (or K-3) furnished late or missing required information can draw a $340 penalty under IRC 6722, rising to $680, or 10% of the items if greater, when the requirement is intentionally disregarded (2025 instructions). The $340 figure also applies to statements due in 2027 (Rev. Proc. 2025-32).
• Corrections. Fixing a K-1 after the return is filed means an amended Form 1120-S with amended K-1s, covered in how to amend a business tax return.

Why the K-1 date matters for shareholders’ own returns

A shareholder reports K-1 items on the return for the shareholder’s tax year in which the S corporation’s year ends (IRC 1366(a)(1)). For calendar-year owners, 2025 K-1 amounts belong on the 2025 Form 1040, due April 15, 2026. That creates a gap whenever the corporation extends:

• The corporation files in September, the owner is due in April. A shareholder still waiting on a K-1 files Form 4868 by April 15 for 6 more months, to October 15, 2026 for most 2025 calendar-year taxpayers, and pays what they expect to owe by April 15, since Form 4868 does not extend the time to pay.
• One month of slack. The corporation’s extended date, September 15, sits one month before the shareholder’s, October 15. A K-1 that arrives on September 15 leaves 30 days to finish the personal return.
• Consistency. Shareholders must report S corporation items the way the corporation reported them, or tell the IRS they are not (IRC 6037(c)). If the corporation has not filed or furnished the K-1 by the shareholder’s own deadline, including extensions, the Form 8082 instructions direct the shareholder to file Form 8082 to notify the IRS.
• Credits flow the same way. An R&D credit reaches shareholders in box 13, code M, of the K-1 (Form 6765 instructions), but the qualified small business payroll tax election is made at the entity level (IRC 41(h)(4)(C)) on the corporation’s timely filed return, including extensions. For calendar-year 2025, that window closed September 15, 2026; for 2026, the five-question payroll credit eligibility check covers the qualifying tests.

Extending Form 1120-S with Form 7004

Form 7004 with code 25, filed by March 16, 2026 for a 2025 return or March 15, 2027 for a 2026 return, extends the Form 1120-S due date by 6 months to September 15. It extends only the return named on line 1 and does not extend the time to pay. Publication 509 also tells S corporations to deposit what they estimate they owe when they file Form 7004. Some do owe tax: the built-in gains tax, the excess net passive income tax and investment credit recapture, on which estimated payments are required once they total $500 or more (Form 1120-S instructions). Any such tax still owed is due by March 16, 2026 or March 15, 2027, and paying it later adds 0.5% of the unpaid amount per month, up to 25%. The Form 7004 guide covers the lines, e-filing and mailing addresses.

The late filing penalty: per shareholder, per month

IRC 6699 charges an S corporation that files late, counting from the due date as extended, or files a return missing required information. The penalty is a fixed dollar amount “for each month (or fraction thereof) during which such failure continues (but not to exceed 12 months),” multiplied by “the number of persons who were shareholders in the S corporation during any part of the taxable year.” Four features set it apart:

• The amount is indexed. The statute says $195; inflation adjustments make it $255 for returns required to be filed in 2026 (Rev. Proc. 2024-40) and $260 for returns required to be filed in 2027 (Rev. Proc. 2025-32).
• No tax needs to be due. It applies to an S corporation with nothing to pay. If tax is due, the instructions add 5% of the unpaid tax per month, up to 25%, and a minimum for returns more than 60 days late: the smaller of the tax due or $525 for returns filed in 2026.
• Former shareholders count. Someone who sold out in February is still one of the persons who were shareholders during the year.
• It is assessed directly. The IRS assesses it against the corporation without the deficiency procedures that apply to income tax adjustments (IRC 6699(c), (d)).

Illustration for a hypothetical calendar-year S corporation with 3 shareholders and no tax due:

The second row is why an extension is worth filing even when the return may still run late: the clock starts after September 15 instead of March 16. For a 2025 return still unfiled after September 15, 2026, filing by October 15 keeps the count at one month.

Getting the penalty removed

The IRS decides reasonable cause after it sends a penalty notice; the Form 1120-S instructions say not to attach an explanation to the return. There is also administrative relief. The IRS lists the IRC 6699(a)(1) penalty among those eligible for First Time Abate and its replacement, Automatic Exemption from Penalty (IRS administrative penalty relief), which starts with 2025 returns (IR-2026-83). The IRS procedural update of June 17, 2026 lists Form 1120-S among the returns it applies to, provided the return is filed within 3 years of its original due date (SBSE-20-0626-0643). The qualifying record is 3 prior years of the same return filed on time with no penalties other than for estimated tax. The $340 K-1 penalty is not on the relief list.

Sources: 26 U.S.C. 6072(b), returns of partnerships and S corporations; 26 U.S.C. 6037, return of S corporation; 26 U.S.C. 6699, failure to file S corporation return; 26 U.S.C. 1366, pass-through of items to shareholders; IRS, 2025 Instructions for Form 1120-S; IRS, Instructions for Form 2553 (Rev. December 2020); IRS, Instructions for Form 6765 (Rev. December 2025); 26 U.S.C. 41(h), payroll tax election for qualified small businesses; IRS Publication 509 (2026), Tax Calendars; IRS, Instructions for Form 8082 (Rev. October 2025); IRS, Form 4868 (2025) and instructions; IRS, Rev. Proc. 2024-40 (amounts for returns filed in 2026); IRS, Rev. Proc. 2025-32 (amounts for returns filed in 2027); IRS, IRM procedural update SBSE-20-0626-0643, Automatic Exemption from Penalty (June 17, 2026); IRS, IR-2026-83, automatic penalty relief (July 8, 2026); IRS, Administrative penalty relief (reviewed July 14, 2026). Rules, dates and amounts checked against these sources in September 2026. This is general information, not tax advice for your situation. Tax services are provided by licensed tax professionals under a separate engagement agreement. BEG does not provide tax advice.