Capital Gains Tax on Shares: US vs UK Rules for 2026

Sell a share for more than you paid and you have made a capital gain. Depending on where you live and how long you held, some of that profit belongs to the taxman. Capital gains tax on shares is the single most overlooked cost in investing, and in 2026 it looks very different on each side of the Atlantic.

This guide breaks down exactly what US and UK investors owe on share profits in 2026, the numbers that decide your bill, and the legal levers that shrink it. If you are building a long-term portfolio, it pairs well with a structured course on index and ETF investing. One caveat up front: this is education, not personal tax advice, and the rules change with residency and each Budget.

What is capital gains tax on shares?

Capital gains tax on shares is the tax you pay on the profit when you sell shares for more than they cost. The taxable gain is the sale price minus your purchase price and costs — you are taxed on the profit, not the whole sale, and only once you actually sell.

Two things decide the size of the bill: your country of tax residence and, in the US, how long you owned the shares. Everything else in this guide flows from those two facts. Dividends are taxed separately — if that is your question, see our breakdown of the tax basics of buying US stocks from the UK.

When do you actually owe it — at sale or while you hold?

You owe capital gains tax only when you realise the gain by disposing of the shares. A "disposal" means selling, gifting (in most cases), or swapping them. Rising prices in your account create an unrealised gain that carries no tax until you sell.

Here is the catch that surprises new investors: selling and immediately reinvesting the proceeds into a different share still counts as a disposal. The tax is triggered by the sale, not by what you do with the cash afterwards. Reinvesting does not defer the bill — only holding on does.

This is why timing matters. Choosing when to sell — which tax year, and in the US whether you have crossed the one-year mark — is often worth more than choosing what to sell.

US capital gains tax: short-term vs long-term

The US system rewards patience more bluntly than almost any other. The dividing line is one year. Sell within twelve months and your gain is "short-term," taxed as ordinary income at rates up to 37% in 2026. Hold beyond twelve months and it becomes "long-term," taxed at a preferential 0%, 15% or 20%.

For 2026, the long-term rate a single filer pays is 0% on taxable income up to $48,350, 15% from there to $533,400, and 20% above that. Married couples filing jointly get the 0% band up to $96,700 and the 15% band up to $600,050. Short-term gains get none of this — they simply stack onto your salary and are taxed at your marginal income rate.

The difference is not academic. Consider a $10,000 gain taxed at a 32% short-term bracket versus the long-term rates:

Holding one extra day past the twelve-month mark saves $1,700 on this gain. That is the single most valuable, entirely legal move a US share investor can make — and it costs nothing but patience. Before you sell in month eleven, check whether waiting a few weeks changes your rate.

One more layer catches higher earners. A 3.8% Net Investment Income Tax stacks on top of the rates above once your modified adjusted gross income clears $200,000 (single) or $250,000 (married filing jointly). Those thresholds have not moved since 2013, so more investors drift into them every year.

UK capital gains tax on shares: rates and the £3,000 allowance

The UK does not care how long you held the shares — the rate depends only on your income. For 2026/27, share gains are taxed at 18% if they fall within your basic-rate band and 24% above it. The basic-rate band runs until your income plus gains reach £50,270; gains beyond that point are taxed at 24%.

These rates are recent. On 30 October 2024 the government raised CGT on shares from 10%/20% to 18%/24%, bringing them in line with the rates that already applied to residential property. Anyone using older guidance is working from the wrong numbers.

Every individual gets an annual tax-free slice called the Annual Exempt Amount. For 2026/27 it is £3,000 — and its collapse is the real story:

Source: GOV.UK Capital Gains Tax allowance 2026/27 and reduction history (Autumn Finance Bill 2022); IRS 2026 brackets and Topic No. 559 (NIIT).

Three years ago the allowance was £12,300. It fell to £6,000 for 2023/24 and to £3,000 from 2024/25 — a 75% cut that quietly pulled hundreds of thousands of ordinary investors into paying CGT for the first time. Unused allowance cannot be carried forward, so if you do not use it in a tax year, it is gone.

US vs UK: how the two systems compare

Put side by side, the two regimes reward completely different behaviour. The US pays you to hold; the UK barely notices how long you held but hands you a shrinking annual freebie and a powerful tax-free wrapper.

Source: IRS 2026 brackets and Topic No. 559; GOV.UK Capital Gains Tax rates and allowances 2026/27; Deloitte UK tax tables 2026/27.

The row that matters most is the second-to-last one. The tax-free wrapper is the biggest single lever in both countries — and most investors under-use it. That is where the real planning happens, not in the headline rate. For a deeper look at wrapper choice, see how index funds and ETFs differ on tax efficiency.

How to legally reduce capital gains tax on shares

You cannot dodge the tax, but you can shrink it with tools both tax authorities explicitly allow. These are the levers that do the most work.

The wrappers that shelter gains entirely

In the UK, a stocks and shares ISA lets you invest up to £20,000 a year with every gain free of CGT — no annual limit on the profit, no reporting. In the US, gains inside a 401(k) or IRA grow tax-deferred (or tax-free in a Roth), so selling inside the account triggers no capital gains tax at all. Filling these accounts first is the highest-value habit an investor can build.

The everyday levers stack on top:

• Use the holding period (US): crossing twelve months moves you from ordinary rates to 0/15/20%. Waiting weeks can be worth thousands.
• Use the £3,000 allowance every year (UK): it does not roll over, so realising up to £3,000 of gains annually is a free reset of your cost base.
• Harvest losses: realised losses offset realised gains in the same year in both countries, cutting the taxable total.
• Transfer to a spouse or civil partner (UK): transfers between spouses are tax-neutral, letting a couple use two £3,000 allowances and both rate bands.
• Spread disposals across tax years: selling part now and part after the new tax year uses two annual allowances instead of one.

The 30-day traps on both sides

Every country closes the obvious loophole — sell to bank a loss, then instantly rebuy. In the US, the wash-sale rule disallows a loss if you buy a substantially identical security within 30 days before or after the sale, a 61-day window that even covers purchases in your IRA or by your spouse. The disallowed loss is added to the new shares' cost basis, so it is deferred, not destroyed.

The UK equivalent is the "bed-and-breakfast" rule. Sell and rebuy the same share within 30 days and HMRC matches the sale to the repurchase, cancelling the loss. The legal workaround is "bed and ISA": sell in your general account, then rebuy the same shares inside your ISA, which sits outside the matching rules. Frequent traders should also understand how day-trading gains are taxed in the UK, where activity can shift the tax treatment entirely.

Mistakes investors make with share gains

• Selling in month eleven (US). Cashing out just before the one-year mark can double your rate versus waiting a few weeks.
• Wasting the annual allowance (UK). The £3,000 exemption is use-it-or-lose-it; letting it lapse every year forfeits real, permanent savings.
• Ignoring the wrapper. Holding shares in a taxable account when ISA or retirement-account room is still open pays tax you never needed to owe.
• Triggering the 30-day rules by accident. Rebuying too soon after harvesting a loss quietly cancels the tax benefit you were chasing.
• Forgetting the NIIT (US). High earners budget for 20% and get a surprise 23.8% bill once the surtax applies.

Frequently asked questions

Investing involves risk, including the possible loss of capital, and tax rules vary by residency and change over time. This article is educational content, not investment or tax advice.