How To Calculate Capital Gains Tax

A capital gain is the profit made when a capital asset, such as shares, a fund or property, is sold for more than it cost. The difference between the sale proceeds and the cost basis is the gain, and it is subject to capital gains tax.

The cost basis is everything paid to acquire the asset, including the purchase price, commissions and fees. Improving an asset can add to the basis, which reduces the taxable gain. Accurate records of the basis matter, because an overstated gain means an overstated tax.

The holding period determines the rate. In the United States, an asset held for more than one year qualifies for the long-term rate, which is lower than the ordinary income rate. An asset held for a year or less is short-term and taxed at the ordinary rate.

The distinction is one of the largest tax levers available. For a high earner in a 22 or 24 percent ordinary bracket, the long-term rate may be 15 percent, and for the lowest earners the long-term rate can be zero. Simply waiting past the one-year mark can cut the tax substantially.

Long-term rates are themselves tiered. Depending on total taxable income, the rate may be zero, 15 percent or 20 percent, plus a surtax on investment income for the highest earners. The calculator here takes the rate as an input rather than deriving it.

Only the gain is taxed, not the entire proceeds. Selling an asset for 20,000 that cost 15,000 produces a 5,000 gain, and the tax is charged on the 5,000. The original 15,000 of basis is returned untaxed.

Capital losses can offset capital gains. If an asset is sold at a loss, the loss reduces the gains realised in the same year, and excess losses can offset a limited amount of ordinary income and be carried forward. This makes the realised gain, not the gross sale, the figure that matters.

The after-tax profit is the gain minus the tax. It is the figure that shows what the investor actually keeps, and it is often far lower than the headline gain once tax is applied, particularly for short-term holdings.

Timing can shift a gain between tax years. Realising a gain in a year with lower income may attract a lower rate, and spreading sales across years can keep each year's gain in a lower tier.

Wash sale rules prevent a loss being claimed and the same asset immediately repurchased. Selling at a loss and buying a substantially identical asset within a short window disallows the loss, so the timing of repurchase matters.

Certain assets are treated differently. A principal residence may qualify for a large exclusion of the gain, and some retirement accounts shelter gains entirely until withdrawal. The general rules are a starting point, not a complete picture.

State tax may apply on top of the federal rate, so the total rate on a gain can be higher than the federal figure alone. A complete estimate adds the state layer where it applies.

The calculator takes the cost basis, the proceeds and the holding period, applies the long-term rate when the holding exceeds a year, and reports the gain, the rate applied, the tax and the after-tax profit. It does not determine which rate you qualify for.