How does the 3.8% Net Investment Income Tax (NIIT) work?

The NIIT adds 3.8% on the lesser of your net investment income (such as the capital gain) and the amount your modified AGI exceeds $200,000 (single / head of household), $250,000 (married filing jointly), or $125,000 (married filing separately). These thresholds are statutory and are not indexed for inflation. This calculator adds it automatically when it applies.

How are short-term capital gains taxed in 2025?

Gains on assets held one year or less are short-term and are taxed at your ordinary federal income-tax rate (10% to 37% for 2025) by stacking the gain on top of your other taxable income — not at the preferential 0/15/20% long-term rates.

Does this include state capital gains tax?

This page is federal only. For your state's treatment, use the matching state page (for example, the California, New York, or Washington 2025 capital-gains pages) which adds the state portion on top of these federal figures.

What is the Capital Gains Tax Calculator 2025 — Federal 0/15/20% + 3.8% NIIT?

Free 2025 federal capital gains tax calculator. Applies the 0%/15%/20% long-term rates using the 2025 IRS thresholds, taxes short-term gains as ordinary income, and adds the 3.8% Net Investment Income Tax ($200,000 single / $250,000 joint / $125,000 separate). Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Capital Gains Tax Calculator 2025 — Federal 0/15/20% + 3.8% NIIT

Name: Capital Gains Tax Calculator 2025 — Federal 0/15/20% + 3.8% NIIT
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Capital Gains Tax Calculator 2025 (Federal + NIIT)

This calculator works out your 2025 federal capital gains tax — the 0% / 15% / 20% long-term rates on the IRS 2025 thresholds, ordinary rates for short-term gains, and the 3.8% Net Investment Income Tax for high earners.

Federal long-term gains (assets held over one year) are taxed at 0%, 15%, or 20% by total taxable income. For 2025 the 0% band runs to $48,350 (single) or $96,700 (married filing jointly), 15% up to $533,400 (single) or $600,050 (joint), and 20% above. Short-term gains are taxed at ordinary federal rates. High earners also owe the 3.8% Net Investment Income Tax (NIIT) on the lesser of the gain and modified AGI over $200,000 (single) / $250,000 (joint) / $125,000 (married filing separately).

Enter your gain, other taxable income, filing status and holding period below. Everything runs in your browser — no amounts or personal data are transmitted. For your state’s tax on the same gain, open the matching 2025 state capital-gains page.

Estimate, not tax advice. Excludes state and local taxes and special-rate assets (collectibles, qualified small-business stock, depreciation recapture). Verify at irs.gov.