US Capital Gains Tax Calculator

Understanding US Capital Gains Tax

Capital gains tax is the federal tax you pay when you sell a capital asset — shares, funds, cryptocurrency, a business interest, or real estate — for more than you paid for it. The taxable gain is the sale price minus your cost basis (broadly, what you paid plus qualifying improvements and transaction costs). What makes the US system distinctive, and often misunderstood, is that the rate you pay is not a single flat percentage. It depends on three things at once: how long you owned the asset, how much total income you report for the year, and your filing status. For internationally mobile, high-net-worth individuals, a fourth dimension — another country’s tax on the same disposal — often applies as well.

Short-term versus long-term: why the holding period matters

The single most important variable is the holding period. If you sell an asset you have owned for one year or less, the profit is a short-term capital gain. Short-term gains receive no preferential treatment: they are added to your wages, self-employment income, and other ordinary income, and taxed at the ordinary marginal rates that run from 10% up to 37%. If instead you hold the asset for more than one year before selling, the profit becomes a long-term capital gain, which enjoys the reduced statutory rates of 0%, 15%, or 20%. The gap between the two treatments is enormous. A top-bracket investor can pay 37% on a short-term gain but only 20% on the same gain held a day longer — a difference of 17 percentage points. Disciplined investors therefore watch the calendar closely, because crossing the one-year threshold can be worth more than any single deduction on the return.

How the 0%, 15% and 20% long-term bands actually work

The long-term rates are applied using a “stacking” method that trips up many taxpayers. Your ordinary taxable income is counted first and fills the lower brackets. Your long-term capital gain is then layered on top of that income to decide which of the 0/15/20% bands it falls into. This is why a modest earner can realise a gain entirely at 0%, while a high earner sees the same gain taxed largely at 15% or 20%. Because the gain sits on top of ordinary income, a large disposal can also straddle two bands: part of it taxed at 15% and the remainder pushed into the 20% band. The calculator above reproduces this stacking logic precisely, splitting your gain across the bands so you can see exactly where each dollar is taxed.

Short-term vs long-term treatment at a glance

The 3.8% Net Investment Income Tax

High earners face an additional layer that the headline 0/15/20% figures conceal: the Net Investment Income Tax, or NIIT. Introduced in 2013, it adds 3.8% on net investment income — capital gains, dividends, interest, royalties, and passive rental income — once your modified adjusted gross income (MAGI) exceeds a fixed threshold of $200,000 (single or head of household), $250,000 (married filing jointly), or $125,000 (married filing separately). Crucially, these thresholds have never been indexed for inflation, so each year more taxpayers are drawn into the NIIT net. The tax applies to the lesser of your net investment income or the amount by which your MAGI exceeds the threshold. For a high-net-worth investor, this effectively lifts the top long-term rate from 20% to 23.8% — a figure that should be built into any disposal plan. The calculator adds this automatically once your income and gain push MAGI above the relevant line.

Who this affects most: the cross-border, high-net-worth angle

For Jungle Tax clients, capital gains rarely stop at the US border. US citizens and green card holders are taxed by the IRS on their worldwide gains regardless of where they live, so an American entrepreneur in London or a fund principal splitting time between New York and the UK must report US capital gains tax even on assets sold outside the United States. The same disposal can simultaneously be taxable in the UK under its own capital gains regime, which uses different rates, a different annual exemption, and different rules for calculating the gain. Relief from paying twice usually flows through the foreign tax credit and the US-UK double tax treaty, but the two systems do not line up neatly. Timing differences, currency movements between purchase and sale, differing cost-basis rules, and the interaction with the UK remittance basis can all create traps — or, handled well, genuine planning opportunities. A gain that looks fully sheltered on one side of the Atlantic can create an unexpected bill on the other.

Special asset categories to watch

Not every gain follows the plain 0/15/20% path. Gain on the sale of investment real estate that reflects previously claimed depreciation is “unrecaptured Section 1250 gain,” taxed at a maximum 25% rate, while a principal residence may qualify for the Section 121 exclusion of up to $250,000 of gain ($500,000 for a married couple). Collectibles such as art, wine, and precious metals are taxed at a maximum 28% long-term rate rather than 20%. Qualified small business stock under Section 1202 can, in the right circumstances, be sold with a large portion of the gain excluded entirely. And cryptocurrency is treated as property, so every disposal — including crypto-to-crypto swaps and spending — is a taxable event. These special regimes are outside the scope of the simplified estimate above and are exactly the situations where specialist advice pays for itself.

Practical ways to manage a capital gains bill

Because the US rules are so sensitive to timing and total income, capital gains tax is one of the most plannable taxes there is. The most common levers include holding assets beyond the one-year mark to convert short-term gains into long-term gains; harvesting capital losses to offset gains (with up to $3,000 of net loss usable against ordinary income each year and the balance carried forward); spreading disposals across two tax years to stay within a lower bracket or below the NIIT threshold; realising gains deliberately in a low-income “gap” year to use the 0% band; gifting appreciated assets to family in lower brackets; and, for real estate investors, deferring gain through a Section 1031 like-kind exchange. Each of these has conditions and cross-border complications, which is why the figure this calculator produces should be treated as a starting point for a conversation, not a final answer.