Form 1120-S filing guide for S corporations

If your company has an S corporation election that the IRS has accepted, Form 1120-S is the federal income tax return you file for every year the election stays in effect, whether or not the company owed any tax for the year. The return reports the company's income, deductions, and credits and then assigns each owner a share on a Schedule K-1, so the form behaves more like an information return than a conventional corporate tax return. This guide covers who has to file, what each part of the return reports, when and where it goes, and what a late filing costs, based on the IRS instructions for the 2025 tax year.

Form 1120-S is the annual return of a domestic corporation, or another entity treated as one, whose S election has been accepted and remains in effect. A calendar-year company files it by the 15th day of the third month after year end, which was March 16, 2026 for tax year 2025 because March 15 fell on a Sunday and is March 15, 2027 for tax year 2026, and Form 7004 adds six months to the filing date without adding any time to pay. Because the corporation passes its income through to the owners, it generally pays no federal income tax itself apart from a short list of entity-level taxes, while each owner reports a share of the income on a personal return.

Only a company with an accepted S election files Form 1120-S

The IRS instructions put the filing rule in three conditions: the corporation or other entity elected S corporation status on Form 2553, the IRS accepted the election, and the election is still in effect. The instructions also say not to file Form 1120-S for any year before the year the election takes effect, which means a company that has been filing Form 1120 as a C corporation switches only from the first tax year the election covers. Forming an LLC does not create S corporation status by itself, because an LLC's federal classification depends on its owners and the elections it makes, so an LLC files Form 1120-S only after its Form 2553 election is in effect. Form 2553 generally has to be filed no more than two months and fifteen days after the start of the tax year the election is meant to cover, and the Form 2553 instructions offer relief for late elections that can show reasonable cause.

Eligibility is a separate test, and it applies for as long as the company wants to remain an S corporation. The company must be a domestic corporation, or a domestic entity eligible to elect corporate treatment, with no more than 100 shareholders and one class of stock, and it cannot be an ineligible corporation such as an insurance company or a domestic international sales corporation. Shareholders must be individuals, certain trusts, or estates, so partnerships, corporations, and nonresident aliens cannot own shares.

The nonresident alien rule turns on an owner's US tax status and not on a foreign address or passport, so a US citizen living abroad and a foreign citizen who is a US resident for tax purposes are both allowed. A company with a nonresident alien shareholder cannot be an S corporation, which means it is taxed as a C corporation and files Form 1120, and a US single-member LLC wholly owned by a nonresident alien cannot choose S status at all. When that kind of LLC is a disregarded entity with reportable transactions, it files Form 5472 attached to a pro forma Form 1120 instead, and because Form 5472 turns on reportable transactions with related parties rather than on ownership percentage alone, a corporation with a 25% foreign shareholder does not file it automatically in every year.

The election ends in three ways. It terminates automatically on the day the company stops being a small business corporation, for example by issuing a second class of stock or admitting an ineligible shareholder, and the company attaches a statement giving that date to its final S corporation return. It also terminates after three consecutive years in which the company has accumulated earnings and profits and more than 25% of its gross receipts are passive investment income, and it ends by revocation when shareholders holding more than 50% of the shares consent. After a termination the company can generally re-elect only with IRS consent before the fifth tax year after the first year the termination took effect.

The return reports the company's results once and the owners pay the tax

Form 1120-S does not calculate each owner's tax. It calculates ordinary business income or loss on page 1, states the items that must keep their character on Schedule K, and divides everything among the shareholders on their Schedules K-1. Shareholders must include their share of the income on their own returns whether or not it is distributed, so two owners holding 60% and 40% of a company that earned $200,000 and kept every dollar as working capital would still report $120,000 and $80,000. Unlike most partnership income, S corporation income passed through to a shareholder is not self-employment income and is not subject to self-employment tax, a feature that also explains why the IRS watches how owners are paid.

The corporation itself can still owe tax on the return. Line 23a covers the excess net passive income tax and LIFO recapture tax, line 23b carries the Schedule D tax on built-in gains, and line 23c totals them and picks up certain additional items, such as recapture reported on Form 4255 and look-back interest. When the built-in gains tax, the excess net passive income tax, and the investment credit recapture tax together reach $500, the corporation generally pays estimated tax in four installments, which for a calendar-year company fall on April 15, June 15, September 15, and December 15.

Pay to owners who work in the business is the one figure on the return that the owners control, and the IRS watches it. An S corporation must pay a shareholder-employee reasonable compensation for the services performed before it makes non-wage distributions, and payments to a corporate officer are treated as wages to the extent they are reasonable compensation. The IRS looks at what the owner actually did for the company, and if gross receipts come mostly from the owner's own services it will assume that most of the profit is compensation. In David E. Watson, P.C. v. United States, an accountant who owned his firm took a $24,000 salary in 2002 and 2003 alongside substantial distributions, the district court found that $91,044 constituted his wages in those years, and the Eighth Circuit affirmed. Officer pay goes on line 7, so a company that pays an owner a very small salary next to large distributions should document how it reached the figure from the work performed, because the IRS can recharacterize the distributions as wages and the employment taxes follow.

Each part of the return has a specific job

Page 1 opens with identifying items, including item C for Schedule M-3 information, item F for total assets, item G for the S election, and item H for a final, amended, or terminating return, and then runs from income to tax. Income begins with gross receipts on line 1a and cost of goods sold from Form 1125-A on line 2 and totals on line 6, deductions include officer compensation on line 7, salaries and wages on line 8, and depreciation on line 14 and total on line 21, and line 22 shows ordinary business income or loss, the figure that flows to Schedule K and then to each owner's K-1.

Schedules B and K: Schedule B collects other information, such as the accounting method, interests in other entities, and business interest expense elections, and Schedule K summarizes all shareholders' items, which the IRS requires every S corporation to complete.

Schedules L, M-1, and M-2: Schedule L is the balance sheet per books, Schedule M-1 reconciles book income with income per return, and Schedule M-2 tracks the accumulated adjustments account and related accounts that determine how later distributions are treated. A corporation whose total receipts and year-end assets are each under $250,000 can answer yes to Schedule B question 11 and skip Schedules L and M-1, though not M-2. A corporation with year-end assets of $10 million or more generally must file Schedule M-3, and one with less than $50 million can complete Part I of Schedule M-3 plus Schedule M-1 instead of Parts II and III.

Schedule D and other attachments: Capital gains and built-in gains go on Schedule D (Form 1120-S), and the return picks up other forms as needed, such as Form 8825 for rental real estate and Form 4797 for sales of business property.

Schedules K-2 and K-3: These report international items, and the 2025 instructions provide a small S corporation exception (total receipts and year-end assets each under $250,000) and an expanded domestic filing exception that no longer requires filing in later years unless a shareholder asks. Both depend on notifying shareholders, at the latest when the K-1 is furnished, that they will not receive Schedule K-3 unless they request it, and a request received on or before the date one month before the corporation files brings the filing requirement back. A company with no foreign operations can therefore still complete K-2 and K-3, because a shareholder may need the information to compute a foreign tax credit.

The IRS prescribes the attachment order behind page 5, starting with Form 8825, Form 1125-A, and Schedule D, continuing through Form 4797 and the Schedules K-1, with supporting statements last and each one carrying the corporation's name and EIN. Complete every applicable entry space instead of writing "See Attached" or "Available Upon Request."

Schedule K-1 is the part your owners actually rely on

Schedule K summarizes every shareholder's items for the corporation, and a Schedule K-1 reports one shareholder's share. Each person who was a shareholder during the year gets a K-1, the corporation attaches a copy of each to the return filed with the IRS and keeps one for its records, and the regular deadline for giving shareholders their copies follows the return's third-month due date. The K-1 starts with ordinary business income in box 1 and then sorts the share into the categories the owner needs, from rental income and capital gains to section 179 deductions, credits, international items, stock basis items such as distributions, and other information such as the qualified business income details under code V.

Income is generally allocated per share, per day, so an owner who buys or sells shares during the year receives a day-weighted portion, and certain qualifying transactions allow an election to close the books for allocation purposes.

Each category stays separate because it lands on a different part of the owner's return, and the at-risk and passive activity limits apply to each shareholder rather than to the corporation, so a corporation with more than one activity reports items separately by activity. Shareholders apply loss limits in a set order, starting with basis on Form 7203 and then at-risk, passive activity, and excess business loss, which means a loss on a K-1 is not automatically deductible. Form 7203 is required in specified situations, such as claiming an aggregate S corporation loss, receiving a non-dividend distribution, disposing of stock, or receiving a shareholder-loan repayment, and stock basis and debt basis are figured separately, with a loan guarantee creating debt basis only to the extent the shareholder pays on it.

One new code for 2025 matters to companies that spend money on development. The One Big Beautiful Bill Act added section 174A, which allows a deduction for domestic research and experimental expenditures paid or incurred in tax years beginning after 2024, or an election to capitalize and amortize them over at least 60 months. The corporation reports them with code BA on Schedule K, line 17d, the K-1 carries the same code in box 17, and each shareholder's share of section 59(e) expenditures goes in box 12 with code J so the shareholder can elect to amortize. For amounts capitalized in tax years beginning after 2021 and before 2025, the instructions point to Revenue Procedure 2025-28 for transition options.

Because the totals on page 1 and the figures on each K-1 come from the same books, we prepare Form 1120-S and every Schedule K-1 together for the US S corporations we serve, working from the ledger we close each month, so that what the company reports and what each owner receives are consistent.

The due date is fixed and an extension only moves the filing date

An S corporation generally has to file Form 1120-S by the 15th day of the third month after the end of its tax year, and when that day falls on a Saturday, Sunday, or legal holiday the return is due on the next day that is not one. For a calendar-year company that date is March 15, which is why the return for tax year 2025 was due on Monday, March 16, 2026, and why the return for tax year 2026 is due on Monday, March 15, 2027. A fiscal-year company counts the same way from its own year end, and a corporation that has dissolved generally files by the 15th day of the third month after the date it dissolved.

Form 7004, filed by the regular due date, gives an automatic six-month extension that moves a calendar-year return to September 15, but it covers the paperwork only, because the corporation must pay any tax due by the regular due date and interest runs on tax paid late even with an extension. Many S corporations owe no entity-level tax, but a company that converted from C corporation status or earns passive investment income should estimate it before the due date and pay with the extension request.

The extended due date for tax year 2025 was September 15, 2026, so a 2025 return that is still unfiled is already accruing penalties, and the sensible course is to file as soon as it is ready and answer any penalty notice with a reasonable-cause explanation instead of attaching one to the return.

E-filing is required at ten returns and paper returns are mailed by location and assets

For returns filed on or after January 1, 2024, an S corporation must e-file Form 1120-S if it files 10 or more returns of any type during the calendar year, counting income tax, employment tax, excise tax, and information returns together. A company that files five Forms W-2, four quarterly Forms 941, and its Form 1120-S has already reached ten, so a single corporate income tax return does not make paper filing acceptable. The IRS can waive the requirement for hardship through a written request to the Ogden Submission Processing Center.

Kansas City or Ogden, depending on assets: For a corporation in Connecticut, Delaware, the District of Columbia, Georgia, Illinois, Indiana, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia, or Wisconsin, a return with total assets under $10 million and no Schedule M-3 goes to the Department of the Treasury, Internal Revenue Service, Kansas City, MO 64999-0013, while a return with assets of $10 million or more, or one that includes Schedule M-3, goes to the Department of the Treasury, Internal Revenue Service, Ogden, UT 84201-0013.

Every other state: A corporation in any other state sends the return to the Department of the Treasury, Internal Revenue Service, Ogden, UT 84201-0013 regardless of assets.

Foreign countries and US territories: A corporation in a foreign country or US territory uses Internal Revenue Service, P.O. Box 409101, Ogden, UT 84409.

Addresses change from year to year, so confirm the current table in the instructions before mailing, and remember that private delivery services cannot deliver to a P.O. box. An authorized corporate officer must sign the return, and a paid preparer must also sign and include a Preparer Tax Identification Number. To correct a filed return, file an amended Form 1120-S with box H(4) checked and a statement identifying each amended line, along with an amended Schedule K-1 for any shareholder whose information changed.

Late filing is billed per shareholder per month

The failure-to-file penalty on this return is built around the number of owners, which makes it unusual among business penalties. For returns required to be filed in 2026, the penalty is $255 for each month or part of a month, up to 12 months, that the return is late or leaves out required information, multiplied by the number of persons who were shareholders at any time during the tax year, and it applies even when no tax is due. A company with three shareholders that files three months late therefore owes $255 times 3 times 3, or $2,295, and the maximum for those three owners over the full 12 months is $9,180.

When tax is due, the IRS adds 5% of the unpaid tax for each month or part of a month the return is late, up to 25%, and the minimum penalty for a return required to be filed in 2026 that is more than 60 days late is the smaller of the tax due or $525. A corporation that does not pay its tax when due can also be charged one-half of one percent of the unpaid tax per month, again up to 25%.

The K-1 carries its own penalty. For each failure to furnish a Schedule K-1 (and Schedule K-3, where applicable) to a shareholder when due, and for each K-1 that omits required information or contains incorrect information, the IRS can impose $340 per K-1, rising to $680 or, if greater, 10% of the aggregate amount of items required to be reported when the requirement is intentionally disregarded. Reasonable cause removes these penalties, but the company has to show it, so keep the shareholder list, compensation records, and K-1 delivery dates documented through the year.

Relief exists and is worth requesting. The IRS lists the S corporation failure-to-file penalty under section 6699(a)(1) among those eligible for First Time Abate, which generally requires that the same return type was filed on time for the prior three years with no penalty assessed, or with any penalty later abated for reasonable cause or IRS error. The corporation requests it by calling the number on the notice or sending a written statement or Form 843, without needing to name the program or attach documents. Abating the return penalty does not remove the separate K-1 penalties automatically, so ask about each penalty on the notice.

Frequently asked questions

Who has to file Form 1120-S?

A corporation or other entity files Form 1120-S if it elected S corporation status on Form 2553, the IRS accepted the election, and the election is still in effect. An LLC files it once its S election is in effect, and no company should file it for a year before the election takes effect. The requirement does not depend on owing income tax, because the late-return penalty can apply even when no entity-level tax is due.

When is Form 1120-S due?

A calendar-year S corporation must file by the 15th day of the third month after year end, which is March 15 or the next business day when that date falls on a weekend or holiday. Tax year 2025 returns were due March 16, 2026, and tax year 2026 returns are due March 15, 2027. Form 7004, filed by the regular due date, adds six months to file but does not extend the time to pay.

Where do I file Form 1120-S?

An S corporation that files 10 or more returns of any type in a calendar year, counting income, employment, excise, and information returns together, must e-file Form 1120-S, and other S corporations can choose to e-file. A paper return goes to Kansas City, MO or Ogden, UT depending on the state of the corporation's principal business and its total assets, or to P.O. Box 409101 in Ogden for a corporation in a foreign country or US territory, so check the current instructions before mailing.

What is Schedule K-1 (Form 1120-S)?

Schedule K-1 shows one shareholder's share of the corporation's income, deductions, credits, and other items, while Schedule K summarizes all shareholders' items for the corporation. The corporation attaches a copy of each K-1 to the return it files with the IRS and gives each shareholder a copy, and shareholders use it to complete their own returns. A K-1 that is not furnished on time or contains incorrect information can bring a $340 penalty per K-1.

What is the penalty for filing Form 1120-S late?

For returns required to be filed in 2026, the penalty is $255 for each month or part of a month, up to 12 months, multiplied by the number of persons who were shareholders during any part of the year. When tax is due the IRS adds 5% of the unpaid tax per month up to 25%, and the minimum for a return more than 60 days late is the smaller of the tax due or $525.

What is the difference between Form 1120 and Form 1120-S?

Form 1120 is filed by C corporations, which pay corporate income tax at the entity level, while Form 1120-S is filed by S corporations, which pass income through to shareholders on Schedule K-1 and generally pay no income tax themselves. A company that has not made an S election, or whose election has ended, files Form 1120. A foreign-owned single-member LLC that files a pro forma Form 1120 with Form 5472 is a separate case and is not a regular C corporation return.