Form 1120 Explained: What It Is, Who Files It, and How It Works (2025-2026)

What Is Form 1120?

Form 1120 is the U.S. Corporation Income Tax Return. Every domestic C corporation — including LLCs that have elected C-Corp status by filing Form 8832 — must file this form annually with the IRS. The return reports the corporation's income, deductions, credits, and tax liability for the year.

Who Must File Form 1120?

Any domestic corporation that is not an S corporation must file Form 1120. This includes traditional corporations formed by filing articles of incorporation, as well as LLCs that have elected to be taxed as C corporations via Form 8832 (Entity Classification Election).

Important distinction: Foreign-owned single-member LLCs that remain as disregarded entities file a simplified pro forma Form 1120 (with zeros) solely as a cover sheet for Form 5472. That is not the same as the full Form 1120 filed by actual C corporations.

The Six Pages of Form 1120

Form 1120 has six pages, each serving a specific purpose:

Page 1: Entity information, income, deductions, taxable income, tax liability, and payments. This is the summary page.

Pages 2–3: Schedule C (dividends received deduction), Schedule J (tax computation and credits).

Pages 4–5: Other Information — critical yes/no questions about ownership, accounting methods, business activities, Form 1099 compliance, and net operating losses.

Page 6: Schedule L (balance sheet), Schedule M-1 (book-to-tax reconciliation), and Schedule M-2 (retained earnings analysis).

The Flat 21% Corporate Tax Rate

Since the Tax Cuts and Jobs Act of 2017, all C corporation taxable income is taxed at a flat 21% federal rate. There are no longer graduated brackets for corporations. This rate applies regardless of how much income the corporation earns.