Form 1120-S: filing the S corp return for 2026

Form 1120-S works like a funnel. Gross receipts go in at the top, then the company subtracts its costs: the owner's salary, the employer half of payroll taxes, rent, software and every other ordinary business expense. What remains is ordinary business income, which the corporation does not pay tax on in most cases. Instead, Schedule K adds up every item that passes to the owners and Schedule K-1 gives each one a share. The quick check below shows how the same profit and salary compare with staying a default LLC.

Who must file, and when

According to the Instructions for Form 1120-S, a corporation or other entity files this return if it elected S status on Form 2553, the IRS accepted the election and the election is still in effect. There is no exemption for a quiet year: a company that earned nothing still files once the status is active. It does not file 1120-S for any year before the election takes effect.

The return is due by the 15th day of the 3rd month after the end of the tax year. For returns covering 2025, the instructions give March 16, 2026, because March 15 fell on a Sunday; for calendar year 2026 the date is March 15, 2027. That is one month before the personal return, on purpose: the owners need their K-1 to file. An extension is requested on Form 7004 by the regular due date. Interest still runs on any tax paid late.

S corporations that file 10 or more returns of any type during the calendar year, counting payroll returns and information returns, must file 1120-S electronically. A one-owner company with four Forms 941, a Form 940, W-2s and a few 1099s can reach that count faster than expected.

Schedule K and the K-1

Schedule K is the summary of every shareholder's share of income, deductions and credits, and every S corporation completes it. Schedule K-1 shows one shareholder's share. A copy of each K-1 is attached to the return and another goes to the shareholder, no later than the day the 1120-S is due. Items that need separate treatment on a personal return, such as charitable contributions, section 179 expense or interest income, are listed apart from ordinary business income.

Two rules surprise new owners. Income passes through whether or not it was distributed: a K-1 that shows $79,986 is taxable even if the money stayed in the business account. And S corporation income is not self-employment income, as the instructions state, so no Schedule SE applies to it; payroll taxes on the salary take that role. The owner reports the K-1 on Schedule E of Form 1040 and pays income tax at personal rates, usually through quarterly estimated payments.

From profit to K-1 in one example

Payroll forms that come with the return

An S corporation with a working owner is an employer, so the income tax return is only part of the paperwork. Publication 15 sets the calendar:

• Form 941, the quarterly payroll return, by April 30, July 31, October 31 and January 31, reporting withheld income tax and both halves of Social Security and Medicare.
• Form 940, the yearly federal unemployment return, by January 31. FUTA is 0.6 % of the first $7,000 of each employee's pay after the state credit, deposited quarterly only once it exceeds $500.
• Form W-2 to the owner and Copy A with Form W-3 to the Social Security Administration, both by January 31.

Deposits of withheld and payroll taxes follow a monthly or semiweekly schedule set by the size of past payroll. Missing them is a separate penalty from anything on the 1120-S.

Penalties for filing late

The late filing penalty is based on the number of owners, not on the tax. For a return with no tax due, it is $255 for each month or part of a month the return is late, for up to 12 months, multiplied by the number of persons who were shareholders at any time during the year. When tax is due, 5% of the unpaid tax per month, up to 25%, is added, and a return due in 2026 that is more than 60 days late has a minimum penalty of the smaller of the tax due or $525. Each K-1 not given to a shareholder on time, or given with missing or wrong information, can draw a separate $340 penalty. Reasonable cause can remove a penalty, but it has to be shown.

Filing on time costs less than any line of that table, even with an extension. For the S election itself and its own deadline, see the Form 2553 guide; for the owner's pay that feeds line 7 of the return, see reasonable salary; the S corp overview covers eligibility.