Updated October 16, 2026. Quick answer: Form 1120-S is the U.S. Income Tax Return for an S Corporation. A corporation must file it if it elected S status by filing Form 2553, the IRS accepted the election, and the election remains in effect. For calendar year corporations the 2025 due date is March 16, 2026, and the late penalty is charged for each shareholder for each month.
More IRS forms and schedules for individual filers, read line by line: Form 8911 instructions and Form 3800 instructions.
More IRS forms for employers and business owners, read line by line: Form 720 instructions.
S corporation return (Form 1120-S) for 2025, read line by line: Form 1120-S lines 1a to 6, Form 1120-S lines 23 to 28 and Form 1120-S Schedule M-2.
Partnership return (Form 1065) for 2025, read line by line: Form 1065 lines 1a to 3, Form 1065 lines 4 to 8 and Form 1065 lines 19 to 23.
Schedule D and Schedule E (Form 1040) for 2025, read line by line: Schedule D lines 4 and 5 and Schedule E Part II.
More IRS forms and schedules, read line by line: Form 7004 instructions, Form 8886 instructions and Form 8275 instructions.
Related reading on this site: Form 1065 and 1120-S due date 2027.
What Form 1120-S is
The form’s title is “U.S. Income Tax Return for an S Corporation”. The instructions state its purpose: “Use Form 1120-S to report the income, gains, losses, deductions, credits, and other information of a domestic corporation or other entity for any tax year covered by an election to be an S corporation.”
The reason owners care is where the tax lands. “Shareholders are liable for tax on their shares of the corporation’s income (reduced by any taxes paid by the corporation on income).” Whether the election saves money is a separate calculation, worked on the S corporation election calculator page.
Who must file, and the Form 2553 election
The return follows the election. The instructions list three conditions, all of which must be true.
| Requirement | As printed in the instructions |
|---|---|
| Condition (a) | “it elected to be an S corporation by filing Form 2553” |
| Condition (b) | “the IRS accepted the election” |
| Condition (c) | “the election remains in effect” |
| Timing limit | “Don’t file Form 1120-S for any tax year before the year the election takes effect.” |
| Late election | “If you haven’t filed Form 2553 or didn’t file Form 2553 on time, you may be entitled to relief for a late-filed election to be an S corporation.” |
The election itself is made on a different form: “For details about the election, see Form 2553, Election by a Small Business Corporation, and the Instructions for Form 2553.”
Item G on the return repeats the election deadline: “Form 2553 must generally be filed no more than 2 months and 15 days after the beginning of the tax year the election is to take effect.” “A Form 2553 filed with Form 1120-S will generally be a late election.” The late path is covered on the late S corporation election page.
Once made, the status continues: “Once the election is made, it stays in effect until it is terminated.”
When Form 1120-S is due
The instructions give the rule and the 2026 date for calendar year corporations: “For calendar year corporations, the due date is March 16, 2026 (March 15th falls on Sunday).”
The weekend rule is printed: “If the due date falls on a Saturday, Sunday, or legal holiday, the corporation can file on the next day that isn’t a Saturday, Sunday, or legal holiday.” For a corporation that has dissolved, “A corporation that has dissolved must generally file by the 15th day of the 3rd month after the date it dissolved.”
Schedule K and the shareholders’ Schedule K-1
Income passes through, and it passes through whether or not it is paid out. “Shareholders must include their share of the income on their tax return whether or not it is distributed to them.” The instructions add a contrast with partnerships: “Unlike most partnership income, S corporation income isn’t self-employment income and isn’t subject to self-employment tax.” The self-employment tax rules are on the self-employment tax page.
Schedule K totals everything and Schedule K-1 splits it. “Schedule K is a summary schedule of all shareholders’ shares of the corporation’s income, deductions, credits, etc.” “Schedule K-1 shows each shareholder’s separate share.”
| Schedule K line | Wording on the form |
|---|---|
| 1 | “Ordinary business income (loss) (page 1, line 22)” |
| 2 | “Net rental real estate income (loss) (attach Form 8825)” |
| 4 | “Interest income” |
| 5a | “Ordinary dividends” |
| 7 | “Net short-term capital gain (loss) (attach Schedule D (Form 1120-S))” |
| 8a | “Net long-term capital gain (loss) (attach Schedule D (Form 1120-S))” |
| 9 | “Net section 1231 gain (loss) (attach Form 4797)” |
| 16d | “Distributions (attach statement if required) (see instructions)” |
The split follows ownership percentage. “Each shareholder’s pro rata share items (boxes 1 through 17 of Schedule K-1) are figured by multiplying the corresponding Schedule K amount by the percentage in item G.” The instructions give the example of two 50% shareholders. Illustration, not an IRS example: if Schedule K, line 1, were $200,000, the arithmetic is $200,000 times 50%, which is $100,000 in box 1 for each of them.
The copy goes to two places: “Attach a copy of each Schedule K-1 to the Form 1120-S filed with the IRS.” And on timing, “Schedule K-1 must be provided to each shareholder on or before the day on which the corporation’s Form 1120-S is required to be filed.”
The penalty for filing late
As with a partnership, the penalty is built from the number of owners. The instructions print each case.
| Failure | As printed in the instructions |
|---|---|
| Late return, no tax due | “For returns on which no tax is due, the penalty is $255 for each month or part of a month (up to 12 months) the return is late or doesn’t include the required information, multiplied by the total number of persons who were shareholders in the corporation during any part of the corporation’s tax year for which the return is due.” |
| Late return, tax due | “If tax is due, the penalty is the amount stated above plus 5% of the unpaid tax for each month or part of a month the return is late, up to a maximum of 25% of the unpaid tax.” |
| Late payment | “A corporation that doesn’t pay the tax when due may generally be penalized 1/2 of 1% of the unpaid tax for each month or part of a month the tax isn’t paid, up to a maximum of 25% of the unpaid tax.” |
| Schedule K-1 not furnished or wrong | “a $340 penalty may be imposed with respect to each Schedule K-1 (and Schedule K-3, if applicable) for which a failure occurs.” |
| Intentional disregard | “each $340 penalty is increased to $680 or, if greater, 10% of the aggregate amount of items required to be reported.” |
Illustration, not an IRS example: for a return with no tax due, 3 shareholders and a return 2 months late, the computed amount is $255 times 3 shareholders times 2 months, which is $1,530. The instructions also say how to answer a notice: “Don’t attach an explanation when the corporation’s return is filed.”
Reasonable compensation for owner-employees
Line 7 is where officer pay is reported, and the instructions print a caution about it: “Distributions and other payments by an S corporation to a corporate officer must be treated as wages to the extent the amounts are reasonable compensation for services rendered to the corporation.”
The instructions also say the IRS can adjust when pay is too low: “If a shareholder or a member of the family of one or more shareholders of the corporation renders services or furnishes capital to the corporation for which reasonable compensation isn’t paid, the IRS may make adjustments in the items taken into account by such individuals to reflect the value of such services or capital.” How owners think about salary level is on the reasonable salary page, and the Social Security side is on the S corporation and Social Security page.
Retirement plan lines on the return
The deduction for the corporation’s own plan contributions is on line 17. The instructions describe it: “Enter the deductible contributions not claimed elsewhere on the return made by the corporation for its employees under a qualified pension, profit-sharing, annuity, or simplified employee pension (SEP) or SIMPLE IRA plan or any other deferred compensation plan.”
Deferrals are kept off the salary line: “Don’t include salaries and wages reported elsewhere on the return, such as amounts included in cost of goods sold, elective contributions to a section 401(k) cash or deferred arrangement”. Which plan fits an S corporation owner is compared on the solo 401(k) versus SEP IRA page for S corporation owners.
Which revision applies
The edition read for this page is Form 1120-S (2025) and the Instructions for Form 1120-S (2025), which are the revisions irs.gov served when they were read on 2026-10-16. Check the revision printed on the form you are filing, because a later revision can change the due dates, the penalty amounts and the schedule layout.
Every Form 1120-S line and schedule page in one table
Each row links to the page that reads a line, group of lines or schedule of Form 1120-S. The right column is the summary each page carries.
| Page | What it covers |
|---|---|
| Form 1120-S Lines 1a to 6: Receipts and Total Income (2025) | What goes on Form 1120-S lines 1a to 6 for the 2025 S corporation return: receipts, cost of goods sold, Form 4797, other income and total income. |
| Form 1120-S Lines 7 to 12: Wages, Repairs, Rents, Taxes (2025) | What goes on Form 1120-S lines 7 to 12 for 2025: officer pay, wages, repairs, bad debts, rents and taxes, in the IRS instructions’ own words. |
| Form 1120-S Lines 13 to 22: Interest to Ordinary Income (2025) | What goes on Form 1120-S lines 13 to 22 for 2025: interest, depreciation, depletion, plans, other deductions and ordinary business income. |
| Form 1120-S Lines 23 to 28: Tax, Payments, Amount Owed (2025) | What goes on Form 1120-S lines 23 to 28 for 2025: entity-level taxes, payments, estimated tax penalty, amount owed, overpayment and refund. |
| Form 1120-S Schedule B Questions 1 to 3 (2025) | How to answer Form 1120-S Schedule B questions 1 to 3 for 2025: accounting method, business activity and disregarded entity, trust or estate shareholders. |
| Form 1120-S Schedule B Questions 4 and 5 (2025) | How to answer Form 1120-S Schedule B questions 4 and 5 for 2025: corporations, partnerships and trusts the S corporation owns, and restricted stock and options. |
| Form 1120-S Schedule B Questions 6 to 11 (2025) | How to answer Form 1120-S Schedule B questions 6 to 11 for 2025: Form 8918, OID debt, built-in gain, section 163(j), Form 8990 and the small-corporation test. |
| Form 1120-S Schedule B Questions 13 to 16 (2025) | How to answer Form 1120-S Schedule B questions 13 to 16 for 2025: QSub elections, Forms 1099, qualified opportunity funds and digital assets. |
| Form 1120-S Schedule K Lines 1 to 4 (2025) | What goes on Schedule K lines 1 to 4 of the 2025 Form 1120-S: ordinary business income, rental income and interest income, in the IRS’s words. |
| Form 1120-S Schedule K Lines 5 to 10 (2025) | What goes on Schedule K lines 5 to 10 of the 2025 Form 1120-S: dividends, royalties, capital gains, section 1231 gain and other income, per the IRS. |
| Form 1120-S Schedule K Lines 11 to 13 (2025) | What goes on Schedule K lines 11 to 13 of the 2025 Form 1120-S: the section 179 deduction, charitable gifts, other deductions and credits, per the IRS. |
| Form 1120-S Schedule K Lines 14 to 16 (2025) | What goes on Schedule K lines 14 to 16 of the 2025 Form 1120-S: international boxes, AMT items and items affecting shareholder basis, per the IRS. |
| Form 1120-S Schedule K Lines 17 and 18 (2025) | Form 1120-S Schedule K lines 17a to 17d and the line 18 income (loss) reconciliation for 2025, in the IRS’s own words. |
| Form 1120-S Schedule L: Balance Sheets per Books (2025) | What goes on Form 1120-S Schedule L for 2025: the beginning and end of year balance sheet from the S corporation’s books, in the IRS’s words. |
| Form 1120-S Schedule M-1: Income per Books (2025) | How to complete Form 1120-S Schedule M-1 for 2025: book income reconciled to Schedule K line 18, with the IRS’s wording for each line. |
| Form 1120-S Schedule M-2: Accumulated Adjustments (2025) | What goes on Form 1120-S Schedule M-2 for 2025: the AAA, previously taxed income, accumulated E&P and other adjustments account, in the IRS’s words. |
Common mistakes
- Filing Form 1120-S before the election takes effect. The instructions say not to file Form 1120-S for any tax year before the year the election takes effect, and a Form 2553 filed with the return will generally be a late election.
- Paying distributions and calling them something other than wages. The instructions caution that distributions and other payments to a corporate officer must be treated as wages to the extent the amounts are reasonable compensation for services.
- Counting the penalty without the shareholder headcount. The printed formula multiplies the monthly amount by the total number of persons who were shareholders during any part of the tax year, and each late or incorrect Schedule K-1 carries its own penalty.
Related: late S corporation election and Form 2553, S corporation election calculator, S corporation reasonable salary, S corporation election and Social Security, and solo 401(k) versus SEP IRA for S corporation owners.
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Answer againSources
- Form 1120-S (2025), U.S. Income Tax Return for an S Corporation: https://www.irs.gov/pub/irs-pdf/f1120s.pdf
- Instructions for Form 1120-S (2025): https://www.irs.gov/pub/irs-pdf/i1120s.pdf
Read from the IRS documents linked above on October 16, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.