Capital Gains Tax Calculator

Capital Gains Tax Calculator works out federal tax on an investment sale and shows why holding period matters so much. Short-term gains on assets held a year or less are ordinary income, so the tool stacks the gain on top of your other income and charges the difference in bracket tax. Long-term gains get their own 0%, 15% and 20% rate bands, and crucially those bands are measured on your total stacked income — so the same gain can straddle two rates, which flat-rate calculators miss entirely. The 3.8% Net Investment Income Tax is added automatically when modified income crosses the statutory threshold, a step most simple tools skip. A band-by-band table shows exactly how much of the gain sits in each rate, and a capital loss is recognised and flagged rather than silently treated as zero.

Key Features

• Correct Long-Term Stacking

  Long-term gains are layered on top of ordinary income so the 0/15/20% bands apply where they really fall. A gain can legitimately span two rates.

• Short-Term Marginal Calculation

  Short-term gains are taxed by computing bracket tax with and without the gain. That difference is the true marginal cost, not an assumed top rate.

• Net Investment Income Tax

  Adds the 3.8% NIIT on gains above the statutory income threshold. The threshold is fixed by statute and never indexed for inflation.

• Band-by-Band Breakdown

  Table shows how much of the gain falls in each rate band and the tax for each. Makes the marginal effect of a slightly larger sale obvious.

• Capital Loss Detection

  A sale below cost basis is reported as a loss with the amount, rather than rounding to zero tax with no explanation.

• Net Proceeds Figure

  Shows what you actually keep after tax, not just the tax owed. That is the number that matters when deciding whether to sell.

1. 1

   Enter purchase and sale price

   Use your cost basis including commissions for the purchase price, and net sale proceeds for the sale price.

2. 2

   Choose the holding period

   More than one year is long-term and gets preferential rates. One year or less is short-term and taxed as ordinary income.

3. 3

   Enter your other income

   This decides which rate band the gain lands in, so an accurate figure matters more than most people expect.

4. 4

   Select your filing status

   Rate bands and the NIIT threshold both vary by filing status.

5. 5

   Review the band table

   See exactly how much of the gain is taxed at each rate, plus any NIIT charged on top.

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