UK ISA Calculator (Cash & Stocks and Shares)
See exactly how your ISA grows over time — completely free of UK income tax and capital gains tax. Compare cash ISA rates against expected stock market returns.
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ISA Guide
What should I know about ISA Allowance 2026/27?
The annual ISA allowance is £20,000 per person. You can split this between a cash ISA, stocks and shares ISA, innovative finance ISA, and Lifetime ISA (capped at £4,000). Unused allowance cannot be carried over to the next tax year. Couples can invest £40,000 per year combined — one of the most efficient tax shelters available to UK residents.
What's the difference between Cash ISA and Stocks and Shares ISA?
Cash ISAs offer certainty — your capital is protected and you earn a fixed or variable interest rate. Stocks and shares ISAs invest in the market — historically returning 7–10% annually over long periods, but with year-to-year volatility. For time horizons under 5 years, cash is generally safer. For 10+ years, the historical evidence strongly favours equities despite short-term risk.
What's the key thing to understand about The Lifetime ISA (LISA)?
The Lifetime ISA lets you save up to £4,000 per year and receive a 25% government bonus (up to £1,000 per year). It can only be used to buy your first home (under £450,000) or for retirement from age 60+. Withdrawing for any other reason incurs a 25% penalty — which effectively means losing your bonus plus some of your own contributions.
What's the key thing to understand about Power of ISA Compounding?
Because ISA gains are never taxed, the compounding effect is significantly greater than a taxable account over long periods. A basic rate taxpayer investing £10,000 per year at 7% for 30 years: in an ISA — approximately £944,000. In a taxable account — approximately £755,000 (assuming gains are taxed each year). The difference grows with time and is even larger for higher rate taxpayers.