Capital Gains Tax Calculator — 2025 Federal Estimate
Estimate 2025 US federal tax on short- and long-term capital gains with the 0/15/20% long-term brackets and optional 3.8% NIIT. Free, in your browser.
About Capital Gains Tax Calculator
A capital gains tax calculator is a tool that estimates the 2025 US federal tax you owe when you sell an asset for more than you paid. Gains on assets held one year or less are short-term and taxed as ordinary income at your marginal rate; gains on assets held longer than a year are long-term and use the preferential 0%, 15%, or 20% rates. Those long-term rates are applied by stacking the gain on top of your other taxable income, so the bracket depends on your total income. The calculator also adds the optional 3.8% Net Investment Income Tax where it applies. It runs entirely in your browser and is an estimate, not tax advice.
Use cases
- Compare a sale before or after one year. The single biggest lever on your capital gains bill is the holding period. Selling one day past the one-year mark can move a gain from your ordinary income rate to the lower long-term rate. Enter the gain both ways to see the dollar difference, which often makes it worth waiting a short while before selling an appreciated asset.
- See when long-term gains are taxed at 0%. Many people are surprised that some long-term gains are taxed at 0% federally. If your other taxable income is low, part or all of a long-term gain can fall in the 0% band (up to $48,350 single or $96,700 married filing jointly in 2025). The calculator shows how much of your gain lands in each rate band as you adjust your income.
- Model a large one-time sale. A big sale — a stock windfall, a second property, a business stake — stacks on top of your salary and can push part of the gain into the 15% or 20% band. Because the rate is not a single flat number, seeing where your gain crosses each threshold helps you decide whether to spread a sale across two tax years.
- Check whether the 3.8% NIIT applies. High earners can owe an extra 3.8% Net Investment Income Tax on top of the capital gains rate. It applies to the lesser of your net investment income and the amount your modified AGI exceeds $200,000 (single) or $250,000 (married filing jointly). Toggle NIIT on to see whether it changes your estimate and by how much.
- Set aside money for estimated taxes. Capital gains are not usually withheld the way wages are, so a large gain can create a surprise bill or an underpayment penalty. Using the estimate to set aside cash — or to make a quarterly estimated payment — keeps you from spending money the IRS will later want. The figure here is a planning estimate, so leave a margin.
How it works
- Enter your other taxable income. This is the base the long-term gain stacks on and the figure used to approximate your MAGI for NIIT, so it sets which rate bands your gain falls into.
- Enter the gain and how long you held it. Assets held one year or less are short-term (ordinary rates); over a year are long-term (0/15/20%). Enter each gain with its holding period.
- Pick your filing status. Single, married filing jointly, or married filing separately — this sets the bracket thresholds and NIIT limit that apply to you.
- Toggle the 3.8% NIIT. Turn on Net Investment Income Tax if your income may exceed the threshold; the tool adds 3.8% on the lesser of net investment income and MAGI over the limit.
- Read the estimate and breakdown. The calculator shows short-term tax at your marginal rate, long-term tax split across the 0/15/20% bands, any NIIT, and the combined federal total.
Examples
Input: Single, $30,000 other income, $10,000 long-term gain
Output: $0 long-term tax (0% band)
Other income plus the gain stay under $48,350, so the whole gain sits in the 2025 0% band.
Input: Single, $100,000 other income, $20,000 long-term gain
Output: ≈ $3,000 (15% long-term)
Income above $48,350 puts the gain in the 15% band; 15% of $20,000 is $3,000.
Input: Single, $80,000 other income, $10,000 short-term gain
Output: Taxed as ordinary income at your marginal rate
Held under a year, so the gain gets no preferential rate — it is added to income and taxed at your bracket.
Frequently asked questions
What is the difference between short-term and long-term gains?
Holding period. An asset held one year or less produces a short-term gain, taxed as ordinary income at your marginal rate. Held longer than a year, it is a long-term gain, taxed at the preferential 0%, 15%, or 20% federal rate. The extra day past a year can meaningfully lower the tax.
How are the 0%, 15%, and 20% rates chosen?
By stacking. The long-term gain is placed on top of your other taxable income; the part of the gain within the 0% band (up to $48,350 single / $96,700 MFJ in 2025) is untaxed, the next part is 15%, and amounts above $533,400 single / $600,050 MFJ are 20%. A single gain can span more than one band.
What is the 3.8% Net Investment Income Tax?
It is an extra 3.8% tax on investment income for higher earners. It applies to the lesser of your net investment income and the amount your modified AGI exceeds $200,000 single, $250,000 married filing jointly, or $125,000 married filing separately. The calculator adds it only when you toggle it on.
Does this include state capital gains tax?
No. It estimates US federal tax only. Many states tax capital gains as ordinary income, and a few do not tax them at all, so your total bill may be higher than shown. Check your state's own rules separately.
Does it handle the wash-sale rule or carryover losses?
No. The tool does not model the wash-sale rule, capital-loss carryovers from prior years, the $3,000 net loss allowance, or netting gains against losses. Enter your net gain after any offsets you have already worked out, and reconcile with your tax software or preparer.
How accurate is the estimate?
It is a good approximation for the rate bands, but it uses your other taxable income as a stand-in for the exact stacking and MAGI base, and it does not model collectibles (28%), unrecaptured Section 1250 gain (25%), the AMT, or credits. Treat it as a planning figure, not a filing number.
Is my financial data uploaded anywhere?
No. Every calculation runs in your browser. The income and gain figures you enter are not sent to a server or saved.
Pro tips
- Confirm your exact holding period — one day can change short-term to long-term.
- Enter your gain net of any losses you are allowed to offset before using the tool.
- Remember state tax is not included; add it separately for a full picture.
- Recheck the estimate if your other income changes, since it moves the rate bands.
- Set aside the estimated amount so a gain does not create a surprise bill or penalty.
Reviewed by Ahsan Mahmood · Last updated 2026-07-08 · Part of ZTools.
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