For a calendar-year S corporation, federal income tax return Form 1120-S is due March 16, 2026. The statutory deadline is the 15th day of the third month after the tax year closes, but March 15, 2026 falls on a Sunday, so the filing date rolls to the next business day.1eCFR. 26 CFR 1.6072-2 – Time for Filing Returns of Corporations2Internal Revenue Service. Publication 509 (2026), Tax Calendars That date is only the headline. An S corporation also has payroll returns, shareholder K-1s, contractor 1099s, and estimated tax payments on the owners’ side, and each carries its own deadline.
Form 1120-S Filing Deadline
Every S corporation must file Form 1120-S each year to report income, deductions, and credits, even in a year with a loss or no activity.3Internal Revenue Service. About Form 1120-S, U.S. Income Tax Return for an S Corporation The March deadline sits about a month ahead of the individual April 15 deadline for a reason: shareholders need their K-1 data before they can finish their own returns. The corporation itself generally owes no federal income tax on its profits; those profits pass through to shareholders. The filing obligation is separate from the payment question.
Extending With Form 7004
If the return won’t be ready by March 16, Form 7004 buys an automatic six-month extension, moving the calendar-year deadline to September 15, 2026.4Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns The form asks for the corporation’s EIN, the tax year, and the form being extended. You can submit it through the IRS Modernized e-File system or mail a paper copy to the designated service center.
Two catches. The Form 7004 has to arrive by the original due date; a request postmarked March 17 is late and generally won’t be honored. And the extension only delays the entity return. It does nothing for shareholders, who still owe estimated tax on their share of corporate income by the regular quarterly dates.
Penalties for Filing Late
Filing 1120-S late without an extension gets expensive fast. For returns due in 2026, the penalty is $255 per shareholder for each month or partial month the return is overdue, capped at 12 months. A four-shareholder corporation filing three months late owes $3,060 in penalties. If the return is more than 60 days late, the minimum penalty is the lesser of the tax due or $525.5Internal Revenue Service. Instructions for Form 1120-S (2025)
The IRS can waive the penalty for reasonable cause, which covers events like fires, natural disasters, serious illness, or a system failure that blocked electronic filing. Forgetting the deadline or a preparer’s mistake usually doesn’t qualify.6Internal Revenue Service. Penalty Relief for Reasonable Cause First-time penalty abatement is worth asking about if you’ve had a clean compliance record.
Schedule K-1 to Shareholders
Each shareholder must receive a Schedule K-1 showing their share of the corporation’s income, deductions, and credits.7Internal Revenue Service. Shareholder’s Instructions for Schedule K-1 (Form 1120-S) The K-1 is due no later than the date the corporation files its Form 1120-S. File on time in March and shareholders have a month before April 15. Extend to September and shareholders will likely need to extend their own returns too, since they can’t finish without the K-1.
Quarterly Estimated Tax for Shareholders
Because S corporations don’t withhold income tax from shareholder distributions, each owner pays tax on their share of profits directly, using Form 1040-ES. The four quarterly deadlines are April 15, June 15, September 15, and January 15 of the following year.8Internal Revenue Service. Estimated Taxes You can pay more often than that; what matters is having enough in by each quarterly cutoff.
An underpayment triggers a penalty calculated using the IRS underpayment interest rate applied to the shortfall for each quarter, and it applies even if you end up with a refund at year end.9Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual To Pay Estimated Income Tax
Safe Harbor Rules
You avoid the penalty entirely by hitting one of two safe harbors. Pay at least 90% of your 2026 tax liability through estimated payments and withholding, or pay at least 100% of the tax shown on your 2025 return (assuming it covered a full 12 months).10Internal Revenue Service. Form 1040-ES Estimated Tax for Individuals (2026) Higher earners face a stricter bar: if your 2025 adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the prior-year safe harbor jumps to 110% of your 2025 tax. For shareholders whose income moves with business performance, the prior-year method tends to be easier because you’re basing payments on a number you already have.
Payroll Tax Deadlines
S corporations must pay shareholder-employees a reasonable salary before making non-wage distributions. The IRS can reclassify distributions as wages if compensation looks artificially low.11Internal Revenue Service. S Corporation Compensation and Medical Insurance Issues Once wages are paid, the payroll filing calendar kicks in.
Form 941 Quarterly Returns
Form 941 reports federal income tax withheld from wages plus the employee and employer shares of Social Security and Medicare. It’s due by the last day of the month after each quarter closes:12Internal Revenue Service. Instructions for Form 941
- Q1 (January through March): April 30
- Q2 (April through June): July 31
- Q3 (July through September): October 31
- Q4 (October through December): January 31 of the following year
Deposit all payroll taxes on time during the quarter and you get an extra 10 days to file. The deposits themselves follow either a monthly or semiweekly schedule. If your total payroll tax liability during the lookback period (July 2024 through June 2025 for 2026) was $50,000 or less, deposits are monthly. Above that, semiweekly. New employers start on the monthly schedule for their first calendar year.13Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
W-2s and Federal Unemployment Tax
January 31 is heavy. By that date the corporation must distribute W-2s to employees and file copies with the Social Security Administration.14Social Security Administration. Deadline Dates to File W-2s Form 940, the annual federal unemployment tax return, is also due January 31, though employers who deposited all FUTA tax on time may file by February 10.15Internal Revenue Service. Topic No. 759, Form 940, Employers Annual Federal Unemployment (FUTA) Tax Return
1099 Deadlines for Contractors
If the corporation paid $600 or more to an independent contractor during the year, that payment goes on Form 1099-NEC. The 1099-NEC filing deadline is January 31, with no automatic extension. For miscellaneous payments on Form 1099-MISC, paper filing is due February 28 and electronic filing is due March 31.16Internal Revenue Service. Publication 1099 – General Instructions for Certain Information Returns (For Use in Preparing 2026 Returns)
Any business filing 10 or more information returns in a year must file them electronically, and the 10-return threshold counts all information return types combined. Most S corporations with a mix of employees and contractors clear that number easily.
A Note for Former C Corporations
An S corporation that converted from C corporation status can owe entity-level tax in two situations that are paid with the March return. The built-in gains tax under section 1374 applies at the 21% corporate rate when appreciated assets held at conversion are sold within five years, calculated on Schedule D of Form 1120-S.17Office of the Law Revision Counsel. 26 U.S. Code 1374 – Tax Imposed on Certain Built-in Gains A separate tax under section 1375 applies when the corporation carries accumulated earnings and profits from its C years and more than 25% of gross receipts come from passive sources like interest, dividends, rents, or royalties.18Office of the Law Revision Counsel. 26 U.S. Code 1375 – Tax Imposed When Passive Investment Income of Corporation Having Accumulated Earnings and Profits Exceeds 25 Percent of Gross Receipts A corporation that has always been an S corporation isn’t exposed to either.
Fiscal Year Filers
The IRS requires a calendar year by default, but some S corporations operate on an approved fiscal year under Form 1128.19Internal Revenue Service. Instructions for Form 1128 The rule is the same: Form 1120-S is due the 15th day of the third month after the tax year ends, and Form 7004 adds six months. A corporation with a June 30 year end files by September 15 and can extend to March 15. K-1 timing and every deadline tied to the return shift with the fiscal year.