U.S. corporate taxation sits on two pillars: a federal income tax that generally applies at a flat 21% rate to C corporations, and a layer of state (and sometimes local) business taxes that vary widely by jurisdiction. Below is a concise guide to who owes federal corporate tax, how it’s determined and filed, and a 50-state table of 2025 corporate tax designs and headline rates.

Use this page as a practical primer—not a substitute for advice tailored to your facts.

Federal rules (who owes, elections, tax base, returns & deadlines)

Who must pay corporate income tax?

The federal corporate income tax generally applies to C corporations (including entities that elect to be taxed as corporations) and to foreign corporations on income that is effectively connected with a U.S. trade or business (filed on Form 1120-F). S corporations are pass-through entities for federal purposes and typically don’t pay an entity-level income tax (limited exceptions apply, e.g., built-in gains tax). :contentReference[oaicite:0]{index=0}

Who can elect corporate status (check-the-box)?

Eligible entities (e.g., LLCs) may choose their classification for federal tax: disregarded entity, partnership, or association taxable as a corporation, by filing Form 8832 (or Form 2553 to become an S corporation). Certain entities are “per se” corporations and cannot reclassify. The rules are in the “check-the-box” regulations under Treas. Reg. §301.7701-1 through -3. :contentReference[oaicite:1]{index=1}

How is the federal tax calculated?

The corporate tax is imposed at a flat 21% rate on taxable income after statutory adjustments (interest-limitation under §163(j), depreciation rules, NOL limits, etc.). A new 15% corporate alternative minimum tax (CAMT) applies to “applicable corporations” with average annual adjusted financial statement income (AFSI) over $1 billion (different tests for foreign-parented groups). Guidance and a simplified status method were issued in 2025. :contentReference[oaicite:2]{index=2}

Key mechanics often affecting the base include: (i) §163(j) business-interest deduction limits (generally 30% of ATI, with special exceptions) computed on Form 8990; (ii) NOL carryforwards limited to offsetting 80% of taxable income (post-TCJA, with special rules); and (iii) bonus depreciation and cost-recovery rules (Congress in 2025 restored 100% bonus for certain property placed in service after Jan. 19, 2025, with transition elections at 40%/60%). :contentReference[oaicite:3]{index=3}

Which returns are filed and when?

Common federal returns include Form 1120 (C corp), Form 1120-S (S corp), and Form 1120-F (foreign corp), among specialized forms (e.g., 1120-REIT, 1120-RIC). For calendar-year filers, Form 1120 is due April 15 (15th day of the 4th month after year-end), and Form 1120-S is due March 15 (15th day of the 3rd month). Foreign corporations without a U.S. office generally file 1120-F by the 15th day of the 6th month after year-end. Form 7004 requests an automatic six-month filing extension; it does not extend time to pay. :contentReference[oaicite:4]{index=4}

Corporations generally must pay quarterly estimated taxes if they expect to owe at least $500, using the worksheet in Form 1120-W. E-filing is widely required for large return filers. :contentReference[oaicite:5]{index=5}

State-level corporate tax table (2025)

States layer their own corporate income taxes, franchise/excise taxes, or gross-receipts-style levies. A handful impose no state corporate income tax (some use gross receipts instead). The table below summarizes 2025 designs and headline (top) rates. Always confirm brackets, base differences, surcharges, and local taxes (e.g., New York City) before filing. Source data drawn primarily from the Tax Foundation’s 2025 survey and state revenue sites, with notable 2025 changes footnoted in the “Design & notes” column. :contentReference[oaicite:6]{index=6}

Notes: Many states have unique bases (e.g., Massachusetts net-worth measure), industry surcharges (e.g., financial institutions), consolidated/combined reporting rules, and local overlays (e.g., NYC). Always confirm up-to-date rates, brackets, and thresholds on official state sites before filing. Key 2025 updates reflected above: NC 2.25%, PA 7.99%, UT 4.50%, GA 5.19%, and NJ top 11.5% for large taxpayers. :contentReference[oaicite:18]{index=18}

FAQ: U.S. Corporate Tax