When Are S Corp Taxes Due With an Extension?

A calendar-year S corporation that files Form 7004 on time gets an automatic six-month extension, moving the Form 1120-S filing deadline from March 15 to September 15. That is the short answer to when S corp taxes are due with an extension, but it comes with an important catch: the extra time applies to the return, not to any tax the corporation owes. Entity-level tax is still due by the original March deadline, and missing that payment date starts the interest clock even if the return itself is filed on time in September.¹

The 2026 Filing Calendar

For the 2025 tax year, the original March 15 deadline lands on a Sunday, so it shifts to the next business day. Any IRS deadline that falls on a Saturday, Sunday, or federal holiday moves the same way.²

March 16, 2026: Original due date for Form 1120-S, the deadline for filing Form 7004 to request an extension, and the deadline to pay any entity-level tax owed.
September 15, 2026: Extended due date for Form 1120-S if Form 7004 was filed on time.
October 15, 2026: Extended due date for shareholders who separately requested a personal extension on Form 1040.

Fiscal-Year S Corporations

Most S corporations use the calendar year, but the IRS allows other tax years in limited situations. A fiscal-year S corp’s original deadline is the 15th day of the third month after its fiscal year ends, and a six-month extension pushes that to the 15th day of the ninth month. A June 30 year-end, for example, produces an original deadline of September 15 and an extended deadline of March 15 of the following year.³

How to Get the Extension

You request the extension by filing Form 7004 on or before the original due date of the return. There is no approval process. If the form is filed properly and on time, the six months are automatic, no signature is required, and the IRS only contacts you if it denies the request.¹

A properly filed Form 7004 does four things:

Identifies the return type as Form 1120-S and provides the corporation’s basic identifying information.
Includes a good-faith estimate of any tax the corporation owes at the entity level.
Is accompanied by payment of that estimated tax by the original deadline.
Reaches the IRS on or before the original return due date.

Form 7004 can be filed electronically or on paper. S corporations that file 10 or more returns of any type during the calendar year, counting income tax, employment tax, and information returns together, are required to e-file Form 1120-S itself.⁴ If you plan to e-file the return, the IRS recommends e-filing the extension too. Sending Form 7004 on paper and then e-filing the return can cause the return to be processed before the extension is recorded, which triggers a penalty notice.¹

What Still Has to Be Paid by the Original Deadline

S corporations are pass-through entities, so most income flows to shareholders and is taxed on their personal returns. The corporation itself can still owe federal tax in two situations, and an extension does not delay when those taxes are due.¹

Built-in gains tax. If the company converted from a C corporation to an S corporation, gains on assets held at the time of conversion may be taxed at the corporate level when recognized within five years, at the highest corporate rate under Section 11(b).⁵
Excess net passive income tax. If the corporation has leftover earnings and profits from its time as a C corporation and more than 25 percent of its gross receipts come from passive investment income such as rents, royalties, or interest, the excess passive income is taxed at the corporate level.⁶

If the corporation expects to owe $500 or more in entity-level tax when the return is filed, it also has to make estimated tax payments during the year.⁷ Most S corporations that have always operated as S corporations and have no accumulated C corporation earnings will not owe entity-level tax at all.⁸ For those companies, the extension is genuinely a filing extension with nothing to pay in March.

What It Costs to Miss the Extended Deadline

An S corporation that misses the extended September deadline faces a penalty for each month or partial month the return is late, up to 12 months. The penalty is per shareholder: the monthly dollar figure is multiplied by the number of people who held shares at any point during the tax year.⁹

The base amount set in the statute is $195 per shareholder per month, adjusted for inflation. For recent filing years the inflation-adjusted figure has been $235 per shareholder per month. A five-shareholder S corporation that files three months late would owe roughly $3,525 in penalties, calculated as three months multiplied by five shareholders multiplied by $235.⁹

How the Extension Ripples Through to Shareholders

Shareholders cannot finish their personal Form 1040 without the Schedule K-1 from the corporation. The corporation has to provide each shareholder with a K-1 by the date the return is due, including any extended deadline.¹⁰ If the corporation uses the full extension, shareholders may not see their K-1s until September 15, which effectively forces them to extend their own returns.

An individual extension pushes the personal filing deadline to October 15.¹¹ That leaves about a month between the extended corporate deadline and the extended personal deadline to fold in the K-1 numbers. Missing the October 15 individual deadline triggers a failure-to-file penalty of 5 percent of the unpaid tax for each month or partial month the return is late, capped at 25 percent.¹²

Shareholder Estimated Tax Is Not Extended

A personal extension delays the filing of the return, not the payment of tax. Shareholders who expect to owe $1,000 or more for the year after withholding and refundable credits generally have to make quarterly estimated tax payments on their share of S corporation income. For the 2026 tax year, those dates are April 15, June 15, and September 15, 2026, and January 15, 2027.¹³ These payments come due even if the K-1 has not arrived yet, so shareholders often estimate their share from prior-year figures or projections.

You avoid an underpayment penalty by meeting one of two safe harbors: paying at least 90 percent of the tax you will owe for 2026 through withholding and estimated payments, or paying at least 100 percent of the total tax shown on your 2025 return. If your 2025 adjusted gross income exceeded $150,000, or $75,000 if married filing separately, the prior-year threshold rises to 110 percent. No penalty applies if the balance due on the return is less than $1,000 after withholding.¹³

1
Internal Revenue Service. Instructions for Form 7004
2
Internal Revenue Service. Starting or Ending a Business 3
3
Internal Revenue Service. Publication 509 (2026), Tax Calendars
4
Internal Revenue Service. Instructions for Form 1120-S
5
Office of the Law Revision Counsel. 26 USC 1374 – Tax Imposed on Certain Built-In Gains
6
Office of the Law Revision Counsel. 26 USC 1375 – Tax Imposed When Passive Investment Income of Corporation Having Accumulated Earnings and Profits Exceeds 25 Percent of Gross Receipts
7
Internal Revenue Service. Estimated Taxes
8
Internal Revenue Service. S Corporations
9
Office of the Law Revision Counsel. 26 USC 6699 – Failure to File S Corporation Return
10
Internal Revenue Service. Shareholder’s Instructions for Schedule K-1 (Form 1120-S)
11
Internal Revenue Service. Get an Extension to File Your Tax Return
12
Taxpayer Advocate Service. Failure to File Penalty Under IRC 6651(a)(1)
13
Internal Revenue Service. Form 1040-ES, Estimated Tax for Individuals