How to Sell Shares in the UK: Capital Gains Tax Explained

Selling shares in the UK is straightforward through your platform. You may owe capital gains tax if your total gains exceed £3,000 in a tax year. Shares held in an ISA are completely exempt from CGT.

The Basic Process of Selling Shares

Most UK investors sell shares through the same platform where they bought them. The mechanics are simple: log into your account, find the holding you want to sell, enter the number of shares or the pound amount, and confirm the sale. The transaction typically settles within two business days (T+2), meaning the cash appears in your account two days after the sale date.

Your platform will show you a preview before you confirm. This displays the current share price, any dealing charges, and the estimated proceeds you'll receive. Double-check the quantity – selling 100 shares versus 1,000 shares is an expensive typo.

Some platforms charge a flat fee per transaction (commonly £5 to £12), while others charge a percentage. If you're selling a small holding, the fee might eat significantly into your proceeds. Calculate whether the sale is worth it, especially if you're selling to realise a small gain or loss.

For shares held in certificate form (rare for most investors today), you'll need to instruct a stockbroker or use a share dealing service. This involves posting your share certificate and completing paperwork. Most modern investors hold shares electronically through nominee accounts, which makes selling much faster.

Understanding Capital Gains Tax on Share Sales

When you sell shares for more than you paid, the profit is a capital gain. The UK gives you an annual capital gains tax allowance – currently £3,000 for the 2024/25 tax year. You only pay tax on gains above this threshold. This allowance applies to all your capital gains combined: shares, funds, property (excluding your main home), and other chargeable assets.

The rate you pay depends on your income tax band. Basic-rate taxpayers pay 10% on gains within the basic-rate band, then 20% on any gains that push them into higher-rate territory. Higher and additional-rate taxpayers pay 20% on share gains. These rates are lower than income tax, which is why long-term investors often prefer capital growth over dividends.

Here's a concrete example. You bought 500 shares in a FTSE 100 company for £2,000. You sell them for £6,000. Your gain is £4,000. Subtract the £3,000 allowance, leaving £1,000 taxable. If you're a basic-rate taxpayer, you owe £100 in CGT (10% of £1,000). If you're a higher-rate taxpayer, you owe £200 (20% of £1,000).

Importantly, you calculate gains on the total proceeds minus the total cost. Your cost includes the purchase price plus any dealing fees you paid when buying. The proceeds are the sale price minus selling fees. Keep records of all transaction confirmations – you'll need these to prove your costs if HMRC asks.

For more detail on how the allowance works and what counts as a chargeable gain, see our guide on capital gains tax on investments.

When You Must Report and Pay

If your total proceeds from selling shares and other assets exceed four times the annual allowance (£12,000 for 2024/25), you must report this to HMRC in a self-assessment tax return, even if you don't owe tax. If your gains exceed the £3,000 allowance, you must also report and pay any tax due.

The deadline for reporting is 31 October (paper return) or 31 January online for the previous tax year (which runs 6 April to 5 April). You pay any CGT owed by 31 January following the end of the tax year. For example, if you sold shares in July 2024 with a taxable gain, you'd report and pay by 31 January 2026.

If you're not already in self-assessment, you need to register. You can do this on GOV.UK. HMRC will send you a Unique Taxpayer Reference (UTR), which can take a few weeks. Don't leave registration until the last minute.

Some investors worry about selling shares near the end of the tax year. If you sell on 4 April, that gain counts in the current tax year. If you wait until 6 April, it counts in the new tax year with a fresh £3,000 allowance. This timing can be useful for tax planning, but never let the tax tail wag the investment dog – if you want to sell for investment reasons, sell.

How ISAs Change Everything

Shares held inside a stocks and shares ISA are exempt from capital gains tax entirely. You can buy, sell, and realise enormous gains without owing a penny of CGT. This is the single biggest advantage of ISAs for long-term investors who expect their holdings to grow substantially.

When you sell shares inside an ISA, the cash stays within the ISA wrapper. You can leave it as cash, reinvest in different shares or funds, or withdraw it. If you withdraw, you free up ISA allowance space permanently – you can't put that specific money back in without using new allowance.

The annual ISA allowance is £20,000 for 2024/25. This is the maximum you can contribute across all ISA types in a tax year. If you have shares in a general investment account (a taxable account) and you're approaching the CGT allowance, consider prioritising future purchases in your ISA. You can't transfer existing shares into an ISA without selling and rebuying, which would trigger any gain.

For most UK investors, using your ISA allowance first makes sense. You eliminate future CGT worries entirely. Learn how to open a stocks and shares ISA if you haven't already, or read about what a stocks and shares ISA actually is to understand the basics.

Calculating Your Gain: Costs and Allowable Expenses

Your capital gain isn't simply sale price minus purchase price. You can deduct certain costs to reduce the taxable amount. Allowable expenses include broker dealing fees, stamp duty (0.5% on UK share purchases), and any other costs directly related to buying or selling the shares.

Here's the formula: Gain = (Sale proceeds - selling costs) - (Purchase price + buying costs). Every pound of allowable costs reduces your taxable gain by a pound, which saves you 10p or 20p in tax depending on your rate.

If you bought the same shares at different times and prices (called a "section 104 holding"), you calculate an average cost. Add up all the money you spent buying shares (including fees), divide by the total number of shares you own, and that's your cost per share. When you sell, multiply the number sold by this average cost. Most platforms calculate this automatically in transaction histories, but double-check for accuracy.

Keep detailed records: contract notes from your broker, bank statements showing payments, and platform transaction confirmations. HMRC can ask for evidence up to six years after the tax year, or up to 20 years if they suspect careless or deliberate errors. A simple spreadsheet with dates, quantities, prices, and fees is usually sufficient.

Losses, Bed-and-ISA, and Tax Planning Strategies

If you sell shares at a loss, you can use that loss to offset gains in the same tax year or carry it forward to future years. You must report losses to HMRC within four years if you want to use them later. This reporting is worth doing even if you have no gains this year – the loss remains available indefinitely once registered.

A common strategy is "crystallising losses" before the tax year ends. If you hold shares that have fallen in value, selling them realises the loss, which you can set against any gains. You can immediately rebuy the same shares if you still want to hold them, though watch for the "bed and breakfast" rule: if you buy back the same shares within 30 days, HMRC uses special rules that may limit the loss.

The "bed-and-ISA" strategy involves selling shares in a general account and immediately rebuying them in your ISA. This uses ISA allowance, triggers any capital gain (or loss) now, and puts the shares in a tax-free wrapper going forward. It's useful if you have shares in a taxable account, available ISA allowance, and either a gain within your £3,000 allowance or a loss you want to register.

Another consideration: married couples and civil partners each have their own £3,000 CGT allowance. If one partner has used their allowance and the other hasn't, transferring shares between spouses is tax-free (no gain or loss arises). The receiving spouse can then sell using their allowance. This only works for transfers between living spouses; different rules apply on death.

Tax planning shouldn't override investment sense, but these strategies can save hundreds of pounds for investors with gains near the allowance threshold. The key is awareness: know what you've sold, track your gains through the tax year, and plan December/March sales accordingly.

Common Mistakes and How to Avoid Them

Many investors don't realise they owe CGT until they receive a letter from HMRC. This happens because they assume their platform will handle tax reporting. Platforms report dividend income to HMRC, but you are responsible for calculating and reporting capital gains yourself. Your platform provides transaction data, but it won't file a tax return for you.

Another mistake is forgetting to include small gains across different assets. The £3,000 allowance covers all capital gains: shares, funds, cryptocurrency, second properties, and other assets. If you sold £2,000 of shares and made £1,500 on cryptocurrency, your total is £3,500, which exceeds the allowance by £500. That £500 is taxable.

Some investors panic-sell when approaching the allowance. If you're £500 below the threshold and your shares have gained £700, you might be tempted to hold off selling. But if your investment case says sell, the tax cost is minor – 10% or 20% of £200 (the excess over the allowance) is £20 to £40. Don't let £30 of tax derail sound investment decisions.

Finally, many investors don't realise the huge advantage of ISAs until after they've built substantial taxable holdings. If you have £30,000 in a general investment account that's grown to £50,000, the £20,000 gain is exposed to CGT when you sell. Starting fresh in an ISA means using next year's £20,000 allowance while leaving the old holding untouched. Consider which approach fits your situation, or read about cash ISAs versus stocks and shares ISAs to understand your options.

This is general information, not personalised financial advice. The value of investments can go down as well as up. Check FCA guidance or speak to a regulated adviser.