2025 Capital Gains Tax Calculator

Selling stock, a rental property, or a business you've held for more than a year? Your long-term capital gain is not taxed at one flat rate — it is stacked on top of your other taxable income and taxed layer by layer across the 0%, 15%, and 20% brackets. This calculator shows exactly where your gain falls, and adds the 3.8% Net Investment Income Tax if your income is high enough to trigger it — using the official 2025 IRS thresholds.

Why "what tax bracket am I in" is the wrong question for capital gains

Most people assume their capital gains rate is simply whatever percentage matches their income bracket. It is close, but the mechanism is different in a way that matters. The IRS looks at your taxable income including the gain and figures out which part of that combined total falls into the 0%, 15%, and 20% capital gains brackets — treating your ordinary income as filling up the lower brackets first, so your gain sits on top. That means the same $50,000 gain can be entirely tax-free for one household and partly taxed at 15% for another, depending on what else they earned that year. The breakdown table above shows this stacking explicitly, bracket by bracket, using your own numbers.

The 3.8% surtax that catches people off guard

Above certain income levels, the Net Investment Income Tax adds an extra 3.8% on top of the capital gains rate — so a gain taxed at 20% can effectively cost 23.8%. The NIIT does not use the same brackets as the capital gains rates; it triggers once your modified adjusted gross income passes $200,000 (single and head of household), $250,000 (married filing jointly), or $125,000 (married filing separately), and applies to whichever is smaller: your net investment income or the amount you're over the threshold. This calculator applies that comparison automatically rather than just multiplying your whole gain by 3.8%, which is a common shortcut that overstates the tax for people near the threshold.

Timing a sale can change your bracket entirely

Because the gain stacks on top of ordinary income, the calendar year you sell in — and what else happens in that year — can swing your rate substantially. Retiring, taking a sabbatical, or having a lower-income year can push a gain that would otherwise be taxed at 15% partly or fully into the 0% bracket. Selling in tranches across two tax years instead of all at once can sometimes keep more of the gain inside the lower brackets. None of this is a reason to delay a sale for the wrong reasons, but it is a reason to run the numbers before, not after, a large sale closes — our guide on capital gains versus wages walks through how these interact with income planning in more detail.