What is Form 1120 (C-Corp Annual Return)?
Form 1120 is the annual federal income tax return for US C-corporations, due 15 April for calendar-year filers (15th day of the 4th month after fiscal year-end for fiscal-year filers). Six-month automatic extension available via Form 7004.
Current Rate (Annual, calendar year default)
N/A — return only
Example
Acme Inc. (calendar year C-corp) files Form 1120 by 15 April 2025 reporting 2024 taxable income, federal corporate income tax, and any tax credits (R&D, foreign tax credit, etc.).
How Form 1120 (C-Corp Annual Return) works in United States
Form 1120 is the C-corporation's annual tax return to the IRS. It reports gross income, deductions, taxable income, and federal income tax owed. It is not a simple short form — a fully-completed 1120 for a complex C-corp can run dozens of pages.
**Filing deadlines**
- Calendar-year C-corps: 15 April (the 15th day of the 4th month after year-end) - Fiscal-year C-corps: 15th day of the 4th month after fiscal year-end - 6-month automatic extension via Form 7004 (to 15 October for calendar year corps)
The extension is for filing only — any tax owed is still due by the original deadline. Paying late triggers interest and failure-to-pay penalties.
**Estimated tax payments**
C-corps with a tax liability of $500 or more must pay estimated taxes quarterly: - 15 April, 15 June, 15 September, 15 December (for calendar-year corps)
Safe harbor: pay 100% of prior year tax OR 100% of annualised current year tax. Large corporations ($1m+ in tax in any of the prior 3 years) must use current-year annualisation — prior year safe harbor is not available.
**Key schedules**
- Schedule C: dividends and special deductions - Schedule J: tax computation and payments - Schedule K: other information (stock ownership, foreign activities) - Schedule L: balance sheet per books - Schedule M-1: reconciliation of book income to taxable income - Schedule M-2: analysis of unappropriated retained earnings - Schedule M-3 (for corps with $10m+ assets): detailed book-tax reconciliation
**Late filing penalty**
5% of unpaid tax per month (or partial month), up to 25% maximum. Minimum penalty applies if the return is more than 60 days late: the lesser of $435 or 100% of unpaid tax.
Related terms
A C-corporation is a US business entity taxed separately from its owners under Subchapter C of the Internal Revenue Code. It pays 21% federal corporate income tax on profits, and shareholders pay personal tax on dividends — the 'double taxation' of C-corp profits. Most VC-backed startups are Delaware C-corps.
Form 1120-S is the annual federal income tax return for US S-corporations, due 15 March for calendar-year filers. The corporation does not pay federal income tax; instead, each shareholder receives a Schedule K-1 reporting their share of income, deductions and credits.
Form 1065 is the annual return for US partnerships and multi-member LLCs taxed as partnerships, due 15 March for calendar-year filers. The partnership does not pay federal income tax; profits flow to partners via Schedule K-1.
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