Capital gains tax sounds like something only millionaires need to understand — until you sell shares, a second property, or a chunk of crypto and HMRC comes calling. CGT is the tax on the profit you make when you sell or dispose of an asset that has increased in value, and it catches far more ordinary people than its reputation suggests. With the annual exempt amount slashed to just £3,000 (2025/26), even modest gains now trigger tax bills. This guide explains CGT from absolute scratch: what it is, when it applies, how it is calculated, and how to legally minimise it.
What Capital Gains Tax Is (and Isn’t)
Capital gains tax is charged on the profit — the gain — when you dispose of an asset, not on the total sale price. Buy shares for £5,000, sell for £8,000: the gain is £3,000. “Dispose” includes selling, giving away, swapping, and in some cases transferring to a spouse (though spouse transfers are generally exempt). It applies to assets including shares and funds (outside ISAs/pensions), second properties and buy-to-lets, business assets, cryptoassets, and valuable personal possessions worth over £6,000 (art, antiques, jewellery — but not cars, which are exempt).
Crucially, CGT does not apply to your main home (Private Residence Relief covers it), ISAs and pensions (all gains tax-free), UK government gilts, betting and lottery winnings, or transfers to a spouse or civil partner. Understanding these exemptions is half the battle — most CGT planning is simply about routing gains through the exempt channels. HMRC’s guidance on tax when selling property and shares pages are the authoritative references.
The Rates and Allowances (2025/26)
Everyone gets an annual exempt amount: £3,000 of gains tax-free per tax year (down from £12,300 just a few years ago — a change that dragged millions into CGT). Gains above this are taxed at rates depending on the asset and your income tax band:
Shares, funds, crypto and most assets: 10% for basic-rate taxpayers, 20% for higher and additional-rate taxpayers (on gains within/falling into those bands). Note the October 2024 Budget raised these from 10%/20% — check current rates, as CGT rates have moved recently.
Residential property (second homes, buy-to-lets): 18% for basic-rate taxpayers, 24% for higher-rate taxpayers. Property CGT must be reported and paid within 60 days of completion via HMRC’s UK property account — miss the deadline and penalties accrue.
Business Asset Disposal Relief (formerly Entrepreneurs’ Relief): a 10% rate on qualifying business disposals up to a £1 million lifetime limit — valuable for business owners selling up.
Your income tax band determines your CGT rate, which creates planning opportunities: realising gains in a low-income year (a sabbatical, early retirement, maternity leave) can halve the rate. If you are building wealth through investing generally, our guide to UK tax bands for the self-employed helps with the income side of the equation.
How Gains Are Calculated (With Examples)
The basic formula: sale proceeds minus purchase cost minus allowable costs (broker fees, stamp duty, solicitor fees, improvement costs — but not routine maintenance) equals the gain. Example: you buy £10,000 of shares, pay £50 in dealing fees, sell for £16,000 paying £50 fees. Gain = £16,000 − £10,000 − £100 = £5,900. Minus the £3,000 annual exempt amount = £2,900 taxable. As a higher-rate taxpayer at 20%, the bill is £580.
Complications arise with: share matching rules (shares bought and sold within 30 days are matched under “bed and breakfast” rules to prevent artificial loss-harvesting); crypto (every crypto-to-crypto trade is a taxable disposal, and HMRC requires meticulous records — pooling rules apply); inherited assets (you inherit at the probate value, so only gains after inheritance count); and gifts (market value at gift date counts, even if no money changed hands — a nasty surprise for generous parents). Keep records of every purchase price, date and cost; reconstructing them years later is miserable.
A worked crypto example shows why records matter so much. Suppose you bought 1 ETH for £1,500 in 2021, another for £2,500 in 2022, then traded 1 ETH for a different token when ETH was £3,000. Under HMRC’s pooling rules, your pooled cost is (£1,500 + £2,500) ÷ 2 = £2,000 per ETH, so the disposal creates a £1,000 gain — even though no pounds changed hands. Multiply this across dozens of DeFi transactions and you see why HMRC-compliant crypto tax software exists: manual calculation becomes genuinely impractical, and the penalties for getting it wrong are real. The HMRC guide to tax on shares covers the matching rules.
Legal Ways to Reduce Your CGT Bill
Use your annual exempt amount every year. The £3,000 allowance is use-it-or-lose-it — it cannot be carried forward. Regularly realising small gains (e.g., rebalancing a portfolio) harvests the allowance annually rather than facing one large taxable gain later.
Use ISAs and pensions. Gains inside ISAs (£20,000 annual allowance) and pensions are entirely CGT-free. “Bed and ISA” — selling assets and rebuying within an ISA — moves future growth into the tax-free wrapper (the sale itself uses that year’s CGT allowance).
Transfer to a spouse. Transfers between spouses/civil partners are CGT-free, effectively doubling the household annual exempt amount to £6,000 and allowing gains to be realised by the lower-rate-taxpayer spouse.
Offset losses. Capital losses can be offset against gains in the same year (or carried forward indefinitely if registered with HMRC). Crystallising a loss on a dud investment to offset a gain elsewhere is legitimate tax planning — just respect the 30-day bed-and-breakfast rule.
Time your disposals. Spread large gains across tax years to use multiple annual allowances, and consider realising gains in lower-income years for the lower rate. For property investors specifically, our guide to self-employed tax and NI covers the income-tax interplay.
Conclusion
Capital gains tax is no longer a rich-person problem: with the allowance at £3,000, anyone selling shares, crypto or property outside tax wrappers needs to understand it. The formula is simple (proceeds minus costs minus allowance), the rates depend on your income band, and the legal minimisation toolkit — annual allowances, ISAs, spouse transfers, loss offsetting, timing — is available to everyone. The expensive mistake is not the tax itself but discovering it after the disposal, when the planning options have expired. Learn the rules before you sell, not after.
Frequently Asked Questions
Do I pay capital gains tax on my main home?
No — Private Residence Relief exempts your main home entirely, provided you lived there throughout ownership. Letting relief and the final 9 months of ownership have additional rules for more complex situations.
How much is the capital gains tax allowance?
£3,000 per person per tax year (2025/26), use-it-or-lose-it. Married couples and civil partners can effectively double this to £6,000 via CGT-free transfers between them.
Do I pay CGT on crypto in the UK?
Yes — cryptoassets are subject to CGT, and every disposal counts, including crypto-to-crypto trades and spending crypto. Only the £3,000 annual exempt amount shields small gains; meticulous records are essential.
When do I need to report capital gains to HMRC?
Property gains must be reported and paid within 60 days of completion. Other gains are reported via Self Assessment by 31 January following the tax year. Register losses with HMRC to carry them forward.
