United States / Guides / Form 1120-S and K-1 timing for S corporations
United States · guideForm 1120-S and K-1 timing for S corporations
The short answer
Form 1120-S for a calendar-year S corporation is due on the 15th day of the third month after the tax year closes — March 15, or the next business day if the 15th falls on a weekend or holiday. Schedule K-1 for each shareholder is due the same date, because the K-1 is generated from the same return and each shareholder needs it to complete their own Form 1040 by April 15. A late-filed 1120-S carries a penalty calculated per shareholder per month, which is why a corporation with several owners can face a penalty far larger than a typical individual late-filing penalty. Form 7004 extends the filing deadline by six months but does not extend the shareholders' need for K-1 data on time for their own returns.
Key facts — verified dates on each
Why the S corporation deadline is earlier than April 15
An S corporation is a pass-through entity: it does not pay federal income tax itself. Instead, each shareholder reports their share of income, deductions, and credits on their personal Form 1040, using the figures the corporation reports on their Schedule K-1. That only works if the shareholder has the K-1 in hand before their own filing deadline.
The IRS built the calendar around that dependency. Partnerships and S corporations — both pass-through entities — file one month ahead of individuals and C corporations. For a calendar-year S corporation, that puts the return and the K-1s due on the 15th day of the third month after year-end, not the fourth. A fiscal-year S corporation follows the same "third month" rule measured from its own year-end.
When the statutory date falls on a Saturday, Sunday, or federal holiday, the deadline moves to the next business day. For the return covering the 2025 tax year, March 15, 2026 falls on a Sunday, so the actual due date is Monday, March 16, 2026.
What has to happen by the deadline
Two things are due on the same date: the corporation's Form 1120-S itself, and a Schedule K-1 for every person who was a shareholder at any point during the tax year — including someone who sold their shares partway through. The K-1 reports that shareholder's pro-rata share of ordinary business income, separately stated items (interest, dividends, capital gains, Section 179 deductions, and similar items that keep their character when they pass through), and other amounts the shareholder needs for their own return.
A shareholder cannot accurately file their Form 1040 without the K-1, which is why the S corporation deadline sits a full month ahead of the individual deadline. That built-in gap gives a shareholder time to receive the K-1 and incorporate it before their own return is due, or to request their own extension if the K-1 arrives late.
Extending the deadline with Form 7004
An S corporation that cannot file on time requests an automatic extension by filing Form 7004 on or before the original due date. For Form 1120-S, this grants a six-month extension — moving the filing deadline for a calendar-year corporation to September 15 (or the next business day if that date falls on a weekend or holiday).
The extension applies to the paperwork, not to any tax the corporation owes at the entity level (state-level entity taxes in some states are a separate matter from the federal pass-through return). It also does not extend the shareholders' own filing deadlines — a shareholder still needs their K-1, or a reasonable estimate, in time to either file or extend their personal return. A corporation that extends its own filing routinely needs to give shareholders estimated K-1 figures or encourage them to file their own extension.
The late-filing penalty and why it scales with shareholder count
Under Internal Revenue Code Section 6699, a late-filed or incomplete Form 1120-S carries a penalty calculated per shareholder per month, not a single flat amount for the corporation. The IRS multiplies a fixed per-shareholder dollar amount by the number of people who were shareholders at any point during the tax year, then by the number of months (or partial months) the return is late, up to a maximum of 12 months. The per-shareholder amount is set by statute and adjusted for inflation each year, so the figure stated in the IRS instructions for the specific return year governs, not a figure carried over from a prior year.
This structure means the penalty grows with the size of the ownership group. A single-shareholder S corporation and a ten-shareholder S corporation that both file three months late face very different total penalties, even though the return itself may be the same size. The penalty applies whether the return is late, or filed on time but missing required information — an incomplete K-1 for even one shareholder can trigger it.
A separate, smaller-magnitude rule applies once a return is more than 60 days late: the minimum penalty becomes the smaller of the tax due or a fixed dollar floor, also inflation-adjusted annually. Because an S corporation typically has no entity-level tax due, that floor rarely helps — the per-shareholder-per-month calculation is usually what applies.
Reasonable cause and how the penalty is addressed
The IRS may abate the Section 6699 penalty for reasonable cause — a showing that the corporation exercised ordinary business care and prudence but still could not file on time, such as a documented natural disaster, serious illness of the responsible party, or reliance on erroneous professional advice given the facts available at the time. Reasonable cause is evaluated case by case and is not automatic; a corporation seeking abatement works with its CPA to prepare and submit the request, since it depends on facts, documentation, and IRS discretion rather than a fixed formula.
The more reliable way to avoid the penalty is to track the deadline and file Form 7004 before the original due date if more time is needed, rather than filing late and requesting relief afterward.
The figures, and when we checked them
These numbers change by year or by notification. Each one shows the date we last verified it against the source — if that date looks old, check the source before relying on it.
Questions on this
When is Form 1120-S due for a calendar-year S corporation?
The 15th day of the third month after the tax year ends. For a calendar-year corporation that is March 15, moved to the next business day when the 15th is a weekend or federal holiday — March 16, 2026 for the 2025 tax year.
Is the Schedule K-1 deadline the same as the Form 1120-S deadline?
Yes. K-1s are generated from the corporation's return and are due to shareholders by the same date the return is due, including any extended due date if the corporation filed Form 7004.
Why is the S corporation deadline a month earlier than the individual deadline?
Because shareholders need the K-1 figures to complete their own Form 1040, due April 15. Putting the pass-through return a month ahead gives shareholders time to receive their K-1 before their own deadline.
How long is the extension if we file Form 7004?
Six months, moving a calendar-year filer's deadline from March 15 to September 15 (or the next business day). Form 7004 must be filed by the original due date.
Does extending the corporate return also extend the shareholders' personal deadlines?
No. Each shareholder's Form 1040 deadline is separate. A shareholder who is still waiting on a K-1 because the corporation extended needs to file their own extension or work from an estimate, with their own preparer.
How is the late-filing penalty calculated?
Per shareholder per month. The IRS multiplies a fixed per-shareholder dollar amount, set by statute and adjusted for inflation each year, by the number of shareholders during the tax year and the number of months or partial months the return is late, up to 12 months.
Does the penalty apply if the return is filed on time but a K-1 is incomplete?
Yes. Section 6699 applies to a return that is late or that fails to include required information, so an incomplete K-1 for even one shareholder can trigger the penalty even if the return itself was filed on time.
Can the late-filing penalty be reduced or removed?
The IRS may abate it for reasonable cause on a case-by-case basis, evaluated against the specific facts and documentation. This is not automatic, and abatement requests are typically prepared with a CPA; filing on time or extending with Form 7004 avoids the issue entirely.
Does a single-shareholder S corporation face the same penalty structure as a multi-shareholder one?
The mechanism is the same, but the total differs because the penalty is per shareholder. A corporation with more shareholders that files late accumulates a larger total penalty than one with fewer shareholders, for the same number of months late.
Where can I check the current per-shareholder penalty amount?
The IRS publishes the current inflation-adjusted figure in the instructions for Form 1120-S for the relevant filing year; the figure changes annually, so a prior year's number does not carry over.
Primary sources
- IRS — Instructions for Form 1120-S
- IRS — Instructions for Form 7004
- 26 U.S.C. § 6699 — Failure to file S corporation return (Cornell Legal Information Institute)
Last reviewed 2026-08-14. Statutes and schedules change — the sources above are authoritative, this page is orientation.
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