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Why this topic matters
Entity Tax Compliance is Area II of Tax Compliance and Planning (TCP). For C corporations, it covers preparing Form 1120 — computing taxable income, reconciling book and tax income on Schedules M-1, M-2, and M-3, handling affiliated and controlled groups, estimated taxes, and key credits and limitations updated by the One Big Beautiful Bill Act (OBBBA).
Form 1120 essentials
- Due the 15th day of the 4th month after year-end (April 15 for calendar years); 6-month extension to file (Form 7004), not to pay.
- Flat 21% rate.
- Schedule L (balance sheet per books), Schedule M-1 or M-3 (book-to-tax reconciliation), Schedule M-2 (retained earnings), and Schedule K (other information).
- Corporations with total assets under $250,000 and gross receipts under $250,000 need not complete Schedules L, M-1, and M-2.
- Schedule M-3 is required for corporations with $10 million or more of total assets — a detailed reconciliation separating temporary and permanent differences.
- The uncertain tax position (UTP) statement, Schedule UTP, applies to corporations with $10 million or more of assets that report uncertain positions in audited financial statements.
Computing taxable income — key items
| Item | Rule |
|---|---|
| Dividends received deduction | 50% (< 20% owned), 65% (20% to < 80%), 100% (80%+); taxable income limit unless a net operating loss (NOL) results |
| Charitable contributions | Deductible only above 1% of taxable income (from 2026) and up to 10%; 5-year carryforward |
| Net operating losses | Indefinite carryforward, 80% of taxable income limit, no carryback |
| Business interest (Section 163(j)) | Limited to 30% of adjusted taxable income computed before depreciation and amortization again (OBBBA, for years beginning after 2024); small businesses (average gross receipts under about $31 million) exempt |
| Research and experimental expenditures | Domestic costs expensed again under new Section 174A (OBBBA); foreign costs amortized over 15 years |
| Depreciation | 100% bonus depreciation permanent for property acquired after January 19, 2025; Section 179 up to $2.5 million (2025, indexed) |
| Capital losses | Only against capital gains; carry back 3, forward 5 |
| Meals and entertainment | Meals 50%; entertainment 0% |
| Compensation | Public companies: $1 million deduction cap per covered employee |
| Organizational and start-up costs | $5,000 each immediately (phase-out above $50,000); rest over 180 months |
EXAMPLE: A corporation's taxable income before the charitable deduction is $1,000,000, and it gave $150,000 to charity in 2026. Floor = 1% × 1,000,000 = $10,000; cap = 10% × 1,000,000 = $100,000. Deduction = $100,000 (contributions above the floor, limited to the cap). The $40,000 above the cap carries forward — and because the 10% cap was exceeded, the $10,000 disallowed by the floor carries forward too, for $50,000 in total. (Floor amounts carry forward only when the cap is exceeded.)
Book-to-tax reconciliation
| Schedule M-1 — additions to book income | Subtractions |
|---|---|
| Federal income tax expense | Tax-exempt interest |
| Excess of capital losses over gains | Tax depreciation above book |
| Income taxed but not booked (prepaid income) | Book income not taxed (life insurance proceeds) |
| Nondeductible expenses (fines, 50% of meals, political contributions) | Deductions not booked (dividends received deduction is taken on page 1) |
| Book depreciation above tax | Charitable carryovers used |
Schedule M-2 = beginning retained earnings + net income per books + other increases − dividends − other decreases = ending retained earnings.
Affiliated and controlled groups
- Consolidated return: an affiliated group (parent owns 80% of vote and value of each subsidiary) may elect to file one return — losses of one member offset income of others; intercompany gains are deferred; intercompany dividends eliminated.
- Controlled groups — parent-subsidiary (80%) and brother-sister (five or fewer individuals own more than 50%, counting only identical ownership) — must share certain limits and thresholds (for example, the accumulated earnings credit, Section 179 limit, and gross receipts tests) even if they file separately.
Estimated taxes
- Due the 15th day of the 4th, 6th, 9th, and 12th months.
- Required annual payment: the lesser of 100% of current-year tax or 100% of prior-year tax (if a 12-month prior year showed a positive tax). Large corporations ($1 million+ taxable income in any of the prior 3 years) may use the prior-year method only for the first installment.
- The annualized income and adjusted seasonal installment methods help corporations with uneven income. The penalty is computed on Form 2220.
Credits and other taxes
- Research credit (Section 41): for qualified research expenses; qualified small businesses may apply up to $500,000 against payroll taxes.
- Foreign tax credit for foreign income taxes, limited to the US tax on foreign-source income.
- General business credits are limited and carry back 1 year and forward 20 years.
- Corporate alternative minimum tax: 15% of adjusted financial statement income for corporations averaging over $1 billion.
- Accumulated earnings tax and personal holding company tax (20% each) discourage retaining earnings to avoid shareholder dividends.
- Many clean energy credits were ended or phased out early by OBBBA.
Accounting methods and periods
- C corporations generally must use the accrual method unless average annual gross receipts are under the small business threshold (about $31 million) — then cash method is allowed, and inventory and uniform capitalization rules are simplified.
- Changing an accounting method generally requires Form 3115 and a Section 481(a) adjustment (unfavorable adjustments spread over 4 years).
How it is tested
- Compute corporate taxable income with the dividends received deduction, charitable floor and cap, and NOLs.
- Complete Schedule M-1 or M-2 from book information.
- Apply consolidated and controlled group rules.
- Compute estimated tax requirements and identify large corporation rules.
EXAM TIP: Schedule M-3 is triggered by assets of $10 million or more, not by revenue. Smaller corporations use Schedule M-1.