What Schedule M-1 does
Books are kept to show investors and lenders how the business performed, usually under US GAAP. Taxable income follows the Internal Revenue Code, which has its own rules on when income counts, which expenses are deductible and how fast assets are written off. The two diverge constantly.
Schedule M-1 makes the gap visible. It begins with net income (loss) per books, adds back items that reduced book income but are not deductible (or income that is taxable but not on the books), subtracts items that increased book income but are not taxable (or deductions the books never took), and ends at the income figure on the return. If the last line does not equal the return, something is missing.
It sits alongside two related schedules: Schedule L, the balance sheet per books, and Schedule M-2, which tracks retained earnings (or partners' capital, or the S corporation accounts) from one year to the next. On Form 1120, book net income on M-1, line 1 is the same figure that flows into M-2. Partnerships and S corporations work differently: their M-2 starts from income per the return, not book income.
Who files M-1, who files M-3, and who files neither
| Return | No M-1 required if | Schedule M-3 required instead if |
|---|---|---|
| Form 1120 (C corporation) | Total receipts and year-end total assets are both under $250,000 (Schedule K, question 13) | Year-end total assets are $10 million or more (consolidated for a group) |
| Form 1120-S (S corporation) | Total receipts and year-end total assets are both under $250,000 (Schedule B, question 11) | Year-end total assets are $10 million or more |
| Form 1065 (partnership) | Total receipts under $250,000, total assets under $1 million, K-1s issued on time, and not filing M-3 (Schedule B, question 4) | Assets of $10 million or more, adjusted total assets of $10 million or more, total receipts of $35 million or more, or a 50% "reportable entity partner" |
Any entity below the M-3 thresholds can file Schedule M-3 voluntarily. REITs, RICs and a few other specialised filers (Forms 1120-REIT, 1120-RIC, 1120-H and 1120-SF) never file Schedule M-3.
Permanent and temporary differences
Every book-tax difference falls into one of two kinds, and the distinction drives both the M-3 columns and the deferred tax on the financial statements.
- Permanent differences never reverse. The item is in book income but will never be in taxable income, or the other way round. Examples: fines and penalties, the nondeductible half of business meals, entertainment, tax-exempt interest, federal income tax expense, and life insurance proceeds.
- Temporary (timing) differences reverse over time. Both systems eventually recognise the same total, but in different years. Examples: depreciation and amortisation, bad debt reserves, accrued bonuses and other accruals paid late, deferred revenue taxed on receipt, capital losses carried forward, and charitable contributions over the limit carried forward.
Schedule M-1 does not ask you to label them; it just needs the total to reconcile. Schedule M-3 does, column by column.
Form 1120 Schedule M-1, line by line
The corporate version has ten lines. Lines 2 to 5 are added to book income; lines 7 and 8 are subtracted.
| Line | What goes there | Typical items |
|---|---|---|
| 1 | Net income (loss) per books | The bottom line of the income statement |
| 2 | Federal income tax per books | Current and deferred federal tax expense, which is never deductible |
| 3 | Excess of capital losses over capital gains | Net capital losses, which a corporation can deduct only against capital gains |
| 4 | Income subject to tax not recorded on books this year | Advance payments taxed on receipt but deferred in the books |
| 5 | Expenses recorded on books this year not deducted on this return | 5a book depreciation above tax depreciation; 5b charitable contributions over the limit; 5c nondeductible travel, meals and entertainment; also fines, bad debt reserves, accrued bonuses paid too late |
| 6 | Add lines 1 through 5 | |
| 7 | Income recorded on books this year not included on this return | Tax-exempt interest, life insurance proceeds |
| 8 | Deductions on this return not charged against book income this year | 8a tax depreciation above book depreciation; 8b charitable contribution carryovers used this year |
| 9 | Add lines 7 and 8 | |
| 10 | Income: line 6 less line 9 | Must equal Form 1120, page 1, line 28 |
Where M-1 stops. Line 10 ties to page 1, line 28: taxable income before the net operating loss deduction and the special deductions such as the dividends-received deduction. So NOL carryovers and the dividends-received deduction never appear on Schedule M-1; they are taken after the point where M-1 ends.
The adjustments you see most often
| Item | Book vs tax | Type |
|---|---|---|
| Depreciation | Books spread cost over useful life; tax uses MACRS and bonus depreciation, usually faster | Temporary |
| Goodwill and acquired intangibles | Books test goodwill for impairment; tax amortises over 15 years under §197 | Temporary |
| Bad debts | Books expense an allowance (reserve); tax deducts only specific debts written off | Temporary |
| Accrued bonuses and related-party expenses | Books accrue them; tax may defer the deduction until paid (for example bonuses paid more than 2½ months after year-end) | Temporary |
| Deferred revenue | Books defer advance payments; tax may include them on receipt or in the following year | Temporary |
| Capital losses | Books deduct them; a corporation deducts them only against capital gains and carries the rest | Temporary |
| Charitable contributions | Books deduct them; tax caps the deduction at 10% of taxable income (and from 2026 also applies a 1% floor) | Temporary (over the cap) or permanent (under the floor) |
| Meals and entertainment | Books deduct them; tax allows 50% of most business meals and no entertainment | Permanent |
| Fines and penalties | Books deduct them; tax disallows them under §162(f) | Permanent |
| Federal income tax | Books expense it; never deductible | Permanent |
| Tax-exempt interest | Books include it; tax excludes it | Permanent |
| Life insurance | Premiums where the company is beneficiary are not deductible; proceeds are generally not taxable | Permanent |
A worked example
A C corporation reports book net income of $800,000. During the year it booked $200,000 of federal income tax expense, had $10,000 more capital losses than gains, received a $30,000 customer prepayment that is taxable now but deferred in its books, paid $15,000 of regulatory fines, had $12,000 of nondeductible meals, increased its bad debt reserve by $25,000, earned $40,000 of municipal bond interest, and claimed $150,000 more depreciation for tax than for books.
| Line | Item | Amount |
|---|---|---|
| 1 | Net income per books | $800,000 |
| 2 | Federal income tax per books (permanent) | +$200,000 |
| 3 | Excess capital losses (temporary) | +$10,000 |
| 4 | Prepayment taxable now, deferred in books (temporary) | +$30,000 |
| 5 | Fines $15,000 and meals $12,000 (permanent); bad debt reserve $25,000 (temporary) | +$52,000 |
| 6 | Subtotal | $1,092,000 |
| 7 | Tax-exempt interest (permanent) | −$40,000 |
| 8a | Tax depreciation above book (temporary) | −$150,000 |
| 9 | Total subtractions | $190,000 |
| 10 | Income per return (page 1, line 28) | $902,000 |
Of the $102,000 net difference, the permanent items (+$200,000, +$27,000 and −$40,000) will never reverse. The temporary ones (+$10,000, +$30,000, +$25,000 and −$150,000) will turn around in later years, and they are what drive the company's deferred tax balances.
Form 1065: what is different for partnerships
The partnership M-1 has nine lines and does not reconcile to ordinary business income. It reconciles to line 1 of the Analysis of Net Income (Loss) per Return, which combines Schedule K, lines 1 through 11, and subtracts lines 12 through 13e and 21. In other words, it reconciles to the total of all the separately stated items that flow to the partners.
- Line 2 adds income that appears on Schedule K but is not in the books.
- Line 3 adds guaranteed payments (other than partners' health insurance). They are deducted in arriving at ordinary business income, but they also appear on Schedule K, line 4 as income to the partners, so net income per return includes them.
- Line 4 adds book expenses not on Schedule K, with depreciation (4a) and travel and entertainment (4b) called out.
- Lines 6 and 7 subtract book income not on Schedule K (tax-exempt interest, 6a) and Schedule K deductions not in the books (depreciation, 7a).
- Line 9 must equal Analysis of Net Income (Loss), line 1.
A partnership has no federal income tax expense to add back, because the partnership itself does not pay federal income tax. Schedule M-2 tracks partners' capital on the tax basis, which must tie to the partners' K-1 capital accounts.
Form 1120-S: what is different for S corporations
The S corporation M-1 has eight lines and follows the partnership model: it reconciles to Schedule K, line 18 (income/loss reconciliation), which combines Schedule K, lines 1 through 10, and subtracts lines 11 through 12e and 16f. Line 2 adds Schedule K income not on the books; line 3 adds book expenses not on Schedule K (depreciation 3a, travel and entertainment 3b); line 5 subtracts book income not on Schedule K (tax-exempt interest 5a); and line 6 subtracts Schedule K deductions not on the books (depreciation 6a).
The S corporation's Schedule M-2 tracks the accumulated adjustments account (AAA), previously taxed income, accumulated earnings and profits, and the other adjustments account, rather than retained earnings.
Schedule M-3 in depth
Schedule M-3 does the same job as M-1, but for larger entities, and in far more detail. It was introduced so the IRS could see the size and nature of each book-tax difference rather than a single net figure. There are separate versions for Forms 1120, 1120-S, 1065 and 1120-F, and separate versions for the two insurance company returns (Forms 1120-L and 1120-PC).
Who must file it
- Corporations (Form 1120): total assets at year-end of $10 million or more, measured on Schedule L. For a consolidated group, it is the total for all includible corporations, net of intercompany eliminations. A corporation that drops below $10 million is not required to file M-3 for that year, even if it filed one the year before.
- S corporations (Form 1120-S): total assets at year-end of $10 million or more.
- Partnerships (Form 1065): any one of total assets of $10 million or more, adjusted total assets of $10 million or more, total receipts of $35 million or more, or a reportable entity partner owning 50% or more of capital, profit or loss on any day of the year. A reportable entity partner is an entity that owns (or is deemed to own) 50% or more of the partnership and was itself required to file Schedule M-3 on its most recent return. It must notify the partnership within 30 days of becoming one.
Relief between $10 million and $50 million. Entities required to file M-3 with less than $50 million of total assets, and those filing voluntarily, may complete Part I of M-3 and then a regular Schedule M-1 instead of Parts II and III. If they do, M-1 line 1 must equal M-3, Part I, line 11. They also skip Schedule B (Form 1120) or Schedule C (Form 1065) and Form 8916-A. At $50 million and above, the whole schedule must be completed.
Part I: which financial statements, and whose income
Part I starts by pinning down which income statement the reconciliation begins from. The order is strict:
- If the company (or its parent) filed a Form 10-K with the SEC for the period, that income statement must be used.
- Otherwise, a certified audited income statement, if there is one.
- Otherwise, any other income statement the company prepared, and only if none exists the books and records.
Where two statements of the same rank exist, the accounting standard decides: US GAAP first, then IFRS, then other international standards, statutory insurance accounting, other regulatory accrual accounting, any other accrual standard, fair value, and cash basis last.
Part I then walks from worldwide consolidated net income on that statement to the net income of only the entities that are actually on the US return. It removes non-includible foreign and US entities, adds includible entities left out of the financial statements, and adjusts for intercompany items and differing year-ends. The result, Part I, line 11, is the starting point for Parts II and III, the M-3 equivalent of M-1's line 1.
Parts II and III: four columns for every line
Part II covers income and loss items and Part III covers expense and deduction items. Every line has four columns:
| Column | What it shows |
|---|---|
| (a) Income (loss) per income statement | The book amount |
| (b) Temporary difference | Differences that will reverse; under GAAP, those that create or change a deferred tax asset or liability |
| (c) Permanent difference | Differences that will never reverse |
| (d) Income (loss) per tax return | The tax amount: (a) plus (b) plus (c) |
If the books follow GAAP, the GAAP treatment decides whether a difference is temporary or permanent. If they do not, the test is practical: a difference you expect to reverse in a later year goes in column (b), and one you do not expect to reverse goes in column (c).
Part II has separate lines for items the IRS cares most about, such as income from equity-method foreign and US corporations, foreign dividends, subpart F, NCTI (formerly GILTI), QEF and PFIC mark-to-market inclusions, foreign tax gross-up, previously taxed distributions, and income from US and foreign partnerships (each partnership listed on a supporting statement). Part III breaks out income tax expense (current and deferred, US and foreign), compensation, stock options, meals and entertainment, fines and penalties, depreciation, amortisation, bad debts, charitable contributions and more. The totals on Part II, line 30 tie column (a) back to book income and column (d) to taxable income on page 1.
The supporting forms
- Schedule B (Form 1120) and Schedule C (Form 1065): additional yes/no questions for M-3 filers.
- Form 8916-A: a breakdown of cost of goods sold, interest income and interest expense in the same four columns.
- Supporting statements for many M-3 lines, naming each entity or item, with columns (a) to (d).
Practical points
- Tie everything out. On Form 1120, M-1 line 1 (or M-3, Part I, line 11) should agree to net income on Schedule M-2; on Form 1065, M-2 picks up income per the return (M-1, line 9) instead. Schedule L should agree to the books. Unexplained breaks in these links are an easy thing for an examiner to spot.
- Itemise. Lines 4, 5, 7 and 8 of the corporate M-1 say "itemize". A single "other" figure with no statement invites questions.
- Partnership M-1s are reconciled to K, not page 1. Most errors come from forgetting guaranteed payments or separately stated items.
- Watch the 2026 changes. The One Big Beautiful Bill Act restored 100% bonus depreciation for property acquired after January 19, 2025 and immediate expensing of domestic research costs under new §174A, both of which widen depreciation and amortisation differences. From 2026, a corporation can deduct charitable gifts only to the extent they exceed 1% of taxable income, up to the 10% cap, and commentators read the amount below the floor as permanently lost.
Sources
- Instructions for Form 1120 (2025), IRS
- Instructions for Form 1065 (2025), IRS
- Instructions for Form 1120-S (2025), IRS
- Instructions for Schedule M-3 (Form 1120), IRS
- Instructions for Schedule M-3 (Form 1065), IRS
- Form 1120 (2025), IRS
- Congress Imposes 1% Floor on Corporate Charitable Deductions, Pierce Atwood
Related reading
- Form 5471 Filer Categories Explained
- Form 8865 Filer Categories Explained
- Glossary: Form 1120
- Glossary: Form 1065
This explainer is analysis and general information, not tax, legal or investment advice.