UK Stock Capital Gains Tax Calculator

CGT on Shares: The 2026/27 Rules

You pay Capital Gains Tax on the profit when you sell shares held outside an ISA or pension, not on the total sale value. Before you buy or sell, you might want to estimate your costs using our Share Dealing Fee Calculator or understand the stamp duty implications using our Shares Stamp Duty Calculator.

The rates for shares rose sharply from 10% and 20% at the October 2024 Budget and now match property rates. The tax free allowance was cut from £12,300 to £3,000 over two years, so far more everyday investors now owe CGT than a few years ago.

How the Calculation Works

Calculating your stock market capital gains tax involves three simple steps:

• Step 1: Find your gain. Sale proceeds minus purchase cost minus dealing fees, stamp duty on both trades. Buy 500 shares for £2,000 and sell for £3,200 and your gain is £1,200 before costs.
• Step 2: Deduct losses and the allowance. Losses from the same year offset first, then subtract the £3,000 annual exempt amount.
• Step 3: Stack the taxable gain on your income. Your gain sits on top of your taxable income. The part still inside the basic rate band (up to £50,270 total) is taxed at 18% and anything above at 24%.

Worked example: salary £40,000, share gain £20,000. Taxable income is £27,430 after personal allowance, leaving £10,270 of basic rate band. The taxable gain after the allowance is £17,000, the first £10,270 at 18% (£1,849), remaining £6,730 at 24% (£1,615). Total CGT roughly £3,464. Earn over £50,270 and the whole taxable gain is simply at 24%.

Section 104: Which Shares Did You Sell?

When you buy the same share at different times, HMRC pools them into a single Section 104 holding with an average cost. Selling part of a holding uses that average, not the price of any specific purchase. Two anti-avoidance rules sit on top: shares bought the same day match first, then any bought within 30 days after the sale (the bed and breakfast rule, which stops you selling and instantly rebuying to bank the allowance).

Legal Ways to Cut the Bill

There are several tax-efficient wrappers and methods you can use to minimize or completely shield your investment growth from capital gains:

• Use the ISA: Gains inside a stocks and shares ISA are entirely CGT free. A Bed & ISA transaction moves existing holdings into the £20,000 annual wrapper. Keep track of how compounding affects these savings over time with our Compound Interest Calculator.
• Split with your spouse: Transfers between spouses and civil partners are CGT free, so a couple can use two £3,000 allowances and both basic rate bands.
• Harvest losses: Losses offset gains in the same year and unused losses carry forward indefinitely if claimed within four years.
• Straddle the tax year: Selling part before and part after 6 April uses two years of allowance.
• Pay into a pension: Contributions extend your basic rate band, shifting gains from 24% to 18% and saving £60 per £1,000 contributed.

Reporting and Paying

Gains above £3,000 go on your Self Assessment return, with tax due by 31 January after the tax year ends, so 2026/27 gains are payable by 31 January 2028. The 60-day reporting deadline applies only to residential property, not shares. Keep contract notes, since HMRC can ask for the full purchase history behind a Section 104 pool. You can also view how dividends affect your tax using our Dividend Tax Calculator.