Tax is the most boring-sounding and most financially impactful aspect of investing. Most people know they're supposed to pay it and broadly how income tax works, but the investment-specific tax rules — capital gains, dividends, the ISA wrapper — are less understood, and getting them right can legitimately change your outcomes by a significant margin.
When you sell an investment for more than you paid, you've made a capital gain. In the UK, gains above the annual CGT allowance are taxable. The allowance has been cut significantly in recent years — it's currently £3,000 per year (2024/25), down from £12,300 in 2022/23.
The CGT rate for investments depends on your income tax band:
CGT is only triggered when you sell. If your investments have risen in value but you haven't sold, you owe nothing. This is one reason long-term investors hold for years rather than trading frequently — unrealised gains accumulate tax-free.
The ISA exception: gains inside a stocks and shares ISA are completely exempt from CGT, regardless of size. This is not a small benefit. An ISA that grows from £20,000 to £200,000 over 30 years creates a £180,000 gain — entirely tax-free. The same investment outside an ISA would face a significant CGT bill when sold. Always use your ISA allowance before investing in a taxable account.
Dividends received outside an ISA are subject to tax above a £500 annual dividend allowance. Rates:
Again, dividends inside an ISA are completely tax-free. If you hold dividend-paying stocks, holding them in an ISA is a no-brainer.
Tax-loss harvesting means deliberately selling investments that are sitting at a loss to create a capital loss, which can be used to offset capital gains. If you've made £10,000 in gains from selling one stock and you have another position sitting at a £4,000 loss, selling it realises a £4,000 loss that reduces your taxable gains to £6,000.
You don't have to stay out of that investment. You can buy something similar (not identical) immediately — or in the UK, you can buy the same investment back after 30 days (the "bed and breakfast" rule). The 30-day rule exists to stop people selling and immediately repurchasing solely for the tax benefit.
A cleaner approach: "bed and ISA." Sell the investment outside an ISA (crystallising either a gain or a loss), then repurchase it inside your ISA using that year's allowance. Any future growth is then sheltered.
The "wash sale rule" is a US concept: if you sell a security at a loss and repurchase the same security within 30 days, the IRS disallows the tax loss. The UK has the 30-day rule which operates similarly. This matters if you're reading American investing content — a lot of tax advice targeted at US investors doesn't apply in the UK.
| Tax event | Inside ISA | Outside ISA (basic rate) |
|---|---|---|
| Capital gain of £10,000 | £0 tax | £700 tax (above £3k allowance) |
| Dividends of £2,000 | £0 tax | ~£131 tax (above £500 allowance) |
| Interest of £1,000 | £0 tax | Subject to income tax |
The tax priority ladder for UK investors: (1) ISA first — fill it every year, no exceptions. (2) SIPP for long-term money you won't need before 57 — tax relief on contributions is essentially a guaranteed return. (3) GIA last — only once ISA is maxed. Within GIA, hold tax-efficient assets (like accumulation ETFs rather than dividend payers) to minimise drag. Getting this order right is worth more than most investment decisions.
A stocks and shares ISA is a tax-free wrapper that lets UK investors hold investments without paying capital gains tax or dividend tax on the returns. You can pay in up to £20,000 per tax year.
A Junior ISA (JISA) is a tax-free account for under-18s, opened by a parent or guardian, with a £9,000 annual allowance. The child can manage it from age 16 but can't withdraw until they turn 18, when it converts to an adult ISA.
No. Growth, interest, and dividends earned inside an ISA are completely free of UK tax — and you don't even need to declare them on a tax return.
Investing as a teenager? Read our guide on how to invest as a teenager in the UK.
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