Understanding Capital Gains Tax in the UK
Capital gains tax (CGT) is levied on the profit you realise when selling an asset for more than you paid for it. The taxable gain is simply the difference between the sale price and the acquisition cost.
UK residents face CGT on a broad range of assets:
- Shares and listed securities
- Investment and second properties
- Cryptocurrency and digital assets
- Antiques, jewellery, and collectibles
- Business assets and goodwill
The amount you owe depends on three key variables: the size of your gain, your total taxable income for the year, and the classification of the asset. Higher earners pay more tax on the same gain because CGT sits above their basic-rate band. Asset type matters because some gains receive preferential treatment—for instance, business asset disposal relief can reduce the effective rate to 10% for qualifying disposals.
Capital Gains Tax Calculation Method
The calculation follows a stepped approach. First, determine your taxable gain by subtracting the acquisition cost from the net sale proceeds. Then subtract the annual exemption allowance (currently £12,300 for the 2024/25 tax year). The remaining amount is taxed at either 10% or 20% depending on whether it falls within your remaining basic-rate band or pushes into higher-rate territory.
Capital Gain = Sale Price − Purchase Price
Taxable Gain = Capital Gain − £12,300 (annual exemption)
Tax Rate = 10% (basic rate) or 20% (higher rate)
Capital Gains Tax = Taxable Gain × Tax Rate
Net Proceeds = Capital Gain − Capital Gains Tax
Sale Price— The amount you received (or are deemed to have received) when disposing of the assetPurchase Price— The amount you originally paid to acquire the asset, plus any incidental costsCapital Gain— The profit calculated as sale price minus purchase priceAnnual Exemption— The tax-free allowance (£12,300 for 2024/25), below which no CGT is dueTax Rate— 10% for basic-rate taxpayers, 20% for higher-rate taxpayers (or 10%/20% for certain asset types with relief)
Tax Allowances and Rate Structure
The current annual exemption threshold is £12,300 per individual for the 2024/25 tax year. Any gain below this amount incurs no tax. Gains above it are taxed progressively based on your income band.
Two main rates apply:
- 10% rate: Applied to gains that fall within your remaining basic-rate band (after accounting for salary, pension, and other income)
- 20% rate: Applied to gains in the higher-rate band (income over £50,270 in 2024/25) or where the gain itself pushes you into higher-rate territory
Trustees managing assets in trust face a single 20% rate with a reduced exemption (£6,150). Business asset disposal relief—available on qualifying business sales—permits a 10% rate regardless of income, subject to lifetime limits of £1 million of gains. Inherited assets receive step-up in basis treatment, meaning no CGT arises on the death of the owner, though subsequent sales by the beneficiary are taxable.
Common Pitfalls and Planning Points
Overlooking these factors can lead to unexpected tax bills or missed opportunities.
- Forgetting to declare gains below the exemption — Even if your gain falls within the £12,300 exemption, you should still report it to HMRC if you're required to file a tax return. Failing to declare can trigger penalties and interest, even though no tax is owed.
- Mixing multiple asset types in one tax year — If you sell shares, property, and crypto in the same year, each may be taxed differently. Some assets (like shares) use the 10%/20% rates; others (like residential property) are subject to separate rules. Stagger sales across tax years if possible to spread gains and make best use of your exemption allowance.
- Ignoring your spouse or civil partner's exemption — Each person has their own £12,300 allowance. Couples can transfer assets between spouses on a no-gain, no-loss basis, or use joint ownership to claim double exemptions. This is especially powerful for investment property or share portfolios.
- Miscalculating acquisition cost — Your purchase price must include stamp duty, broker fees, legal costs, and any improvements (for property). Adding these back reduces your taxable gain. Keep detailed records of all outgoings; HMRC will challenge vague or missing evidence.
Reporting and Compliance
In the UK, reporting capital gains is mandatory if you exceed the exemption threshold. Higher-rate taxpayers must file a self-assessment tax return; basic-rate taxpayers whose income is below £12,570 need not file unless they have gains above £12,300.
The deadline for reporting is 31 January following the end of the tax year in question. Late filing carries penalties starting at £100 and increasing for persistent non-compliance. If tax remains unpaid beyond 30 days of the assessment, interest accrues daily, compounding your bill.
Keep contemporaneous records: purchase invoices, sale contracts, proof of ownership cost, and any supporting valuations or broker statements. HMRC routinely audits large gains and mismatched figures, so poor documentation is a common cause of disputes and additional assessments.