Form 1120-S instructions: a line-by-line guide for reviewers
Form 1120-S is the IRS form an S corporation files each year to report its income, deductions, credits and other items, which pass through to shareholders on Schedule K-1. A calendar-year S corporation's 2025 return is due March 16, 2026.
“Use Form 1120-S to report the income, gains, losses, deductions, credits, etc., of a domestic corporation or other entity for any tax year covered by an election to be an S corporation.” IRS, About Form 1120-S
Who has to file Form 1120-S?
Form 1120-S is filed by a corporation or other entity that elected S corporation status on Form 2553, had the election accepted by the IRS, and still has the election in effect, according to the 2025 Instructions for Form 1120-S. A corporation doesn't file Form 1120-S for any year before the election takes effect. The return is due by the 15th day of the 3rd month after year end, which for calendar-year 2025 returns is March 16, 2026, because March 15 falls on a Sunday.
Three size tests change what the return includes. A corporation with total receipts and year-end total assets both under $250,000 answers Yes to Schedule B, question 11 and skips Schedules L and M-1. One with total assets of $10 million or more files Schedule M-3 instead of Schedule M-1. And total receipts of $500,000 or more require Form 1125-E for officer compensation.
What does a reviewer tie out on the Form 1120-S main page?
Page 1 of Form 1120-S holds only trade or business income and expenses on lines 1a through 22. Rental income, portfolio income and other separately stated items go to Schedule K instead, so much of a page 1 review is checking that each item sits on the right page. Total receipts for the $250,000 and $500,000 tests are wider than line 1a: they add page 1 lines 4 and 5, Schedule K lines 3a, 4, 5a and 6, net gains on Schedule K lines 7, 8a, 9 and 10, and Form 8825 lines 2, 21 and 22a.
| Line | What it is | What a reviewer ties out |
|---|---|---|
| 1a | Gross receipts or sales | Books and records, with amounts that belong on lines 4 and 5 left out |
| 2 | Cost of goods sold | Form 1125-A |
| 4 | Net gain (loss) from Form 4797 | Form 4797, Part II, line 17 |
| 7 | Compensation of officers | Form 1125-E, line 4, when total receipts are $500,000 or more; includes fringe benefits of more-than-2% shareholders |
| 13 | Interest | Leaves out rental interest (Form 8825 or Schedule K, line 3b), investment interest (Schedule K, line 12c) and interest on debt-financed distributions (Schedule K, line 12e, code AC) |
| 14 | Depreciation | Form 4562, less amounts claimed on Form 1125-A or elsewhere |
| 22 | Ordinary business income (loss) | Schedule K, line 1 |
| 23a | Excess net passive income or LIFO recapture tax | Only with C corporation history: accumulated earnings and profits plus passive investment income over 25% of gross receipts |
| Item F | Total assets | Schedule L, line 15, column (d) |
Line 7 carries a caution in the instructions: distributions and other payments to a corporate officer must be treated as wages to the extent they are reasonable compensation for services. Compare line 7 with the shareholder distributions on Schedule K, line 16d, before signing off.
How do Schedules B, K and K-1 tie together?
Schedule K of Form 1120-S totals every pass-through item, and each shareholder's Schedule K-1 is that total multiplied by the item G percentage when ownership didn't change during the year. When it did change, items are allocated daily by shares held, unless all affected shareholders consent to the section 1377(a)(2) election to close the books when a shareholder's interest ends.
Lines 16d (distributions) and 16e (loan repayments) go only on the K-1 of the shareholder who received them, and line 17c dividends from accumulated earnings and profits go on Form 1099-DIV, never a K-1. Line 18 combines lines 1 through 10, less lines 11 through 12e and 16f, and must equal Schedule M-1, line 8. The K-1 item I loan balances should reconcile to Schedule L, line 19. On Schedule B, question 10 sends the corporation to Form 8990 when it has business interest expense and average gross receipts over $31 million, and item 8 reports net unrealized built-in gain. See Schedule K-1 (Form 1120-S).
How do Schedules L, M-1 and M-2 tie out?
Schedule L is the balance sheet per books, Schedule M-1 reconciles book income to Schedule K, line 18, and Schedule M-2 tracks the accumulated adjustments account (AAA) and the other accounts that decide how distributions are taxed. According to the Instructions for Form 1120-S, Schedule L should agree with the books, and its line 15, column (d) total assets is the item F figure on page 1.
Schedule M-1 starts with book net income on line 1, adds Schedule K income not on the books (line 2) and book expenses not on Schedule K (line 3, with nondeductible meals on line 3b), then subtracts book income not on Schedule K, such as tax-exempt interest (line 5), and tax deductions not on the books (line 6). On Schedule M-2, AAA in column (a) goes up by income other than tax-exempt income, down by losses, deductions and nondeductible expenses not related to tax-exempt income, and then down by distributions, which can't take it below zero. See Schedule L and M-2.
What does a Form 1120-S M-1 and AAA tie-out look like?
For example, a calendar-year S corporation with no accumulated earnings and profits has $142,000 of book net income for 2025. Book income includes $3,000 of tax-exempt interest and $2,000 of taxable interest, and is after $4,000 of nondeductible meals and a $5,000 cash charitable contribution. Tax depreciation is $35,000 against $20,000 on the books. AAA at the start of the year is $60,000, and the corporation distributes $100,000.
| Step | Line | Amount |
|---|---|---|
| Net income per books | M-1, 1 | $142,000 |
| Add nondeductible meals | M-1, 3b | $4,000 |
| Subtract tax-exempt interest | M-1, 5a | ($3,000) |
| Subtract tax depreciation above book ($35,000 against $20,000) | M-1, 6a | ($15,000) |
| Income per return | M-1, 8; Schedule K, 18 | $128,000 |
| Ordinary business income (line 18 less $2,000 interest, plus $5,000 contribution) | Page 1, 22; Schedule K, 1 | $131,000 |
| AAA at the beginning of the year | M-2, 1(a) | $60,000 |
| Add ordinary income | M-2, 2(a) | $131,000 |
| Add taxable interest | M-2, 3(a) | $2,000 |
| Subtract contribution and nondeductible meals | M-2, 5(a) | ($9,000) |
| Subtract distributions | M-2, 7(a) | ($100,000) |
| AAA at the end of the year | M-2, 8(a) | $84,000 |
Schedule K, line 18 is $128,000: $131,000 on line 1 plus $2,000 of interest on line 4, less the $5,000 contribution on line 12a. The $3,000 of tax-exempt interest goes on Schedule K, line 16a and in column (d) of Schedule M-2, not AAA, and the $4,000 of meals goes on line 16c. The $100,000 distribution is on line 16d and fits within AAA, so it doesn't reach the other accounts.
What do reviewers check on Form 1120-S?
A reviewer checking Form 1120-S confirms six tie-outs, each from the 2025 Instructions for Form 1120-S. Pull the prior-year return first, because beginning Schedule L balances, beginning AAA on Schedule M-2 and the built-in gain figure in Schedule B, item 8 all carry from it. Then compare the return with the trial balance and the payroll filings: the trial balance supports Schedule L and Schedule M-1, line 1, and payroll supports lines 7 and 8 and Form 1125-E. Last, add up the Schedules K-1. Every pro rata line should sum to Schedule K, and item I loan balances should sum to Schedule L, line 19. Shareholder basis is a separate calculation that the corporation doesn't make, done on each shareholder's Form 7203.
Every line checked against the documents the client sent
Filed reads the trial balance, payroll filings, prior-year return and Schedules K-1, then checks every line of Form 1120-S against them. Anything that doesn't tie comes back as a review item with a citation to the source.
Book a demoSchedule K, line 18 shows $128,000 and Schedule M-1, line 8 shows $131,000. Confirm whether the $3,000 of tax-exempt interest on Schedule K, line 16a was left off Schedule M-1, line 5a.
Common questions
When is Form 1120-S due for 2025?
Form 1120-S for a calendar-year 2025 S corporation is due March 16, 2026, because March 15 falls on a Sunday. The general rule in the Instructions for Form 1120-S is the 15th day of the 3rd month after the tax year ends, and the corporation requests an extension on Form 7004 by that date.
Does every S corporation complete Schedules L and M-1?
No. An S corporation skips Schedules L and M-1 when it answers Yes to Schedule B, question 11, meaning its total receipts for the year and total assets at year end were both under $250,000. A corporation with total assets of $10 million or more files Schedule M-3 instead of Schedule M-1.
Does Form 1120-S track shareholder basis?
No. Form 1120-S tracks corporate accounts such as AAA on Schedule M-2, not shareholder stock or debt basis. The Shareholder's Instructions for Schedule K-1 put basis tracking on the shareholder, who generally uses Form 7203. AAA and stock basis follow different rules, so the two numbers can differ.