ISA calculator
Project how your ISA could grow over time with regular contributions and compound interest. All growth inside an ISA is tax-free.
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Project how your ISA could grow over time with regular contributions and compound interest. All growth inside an ISA is tax-free.
An Individual Savings Account (ISA) is a tax-efficient wrapper available to UK residents. Any interest, dividends, or capital gains earned inside an ISA are completely free from income tax and capital gains tax. You can contribute up to £20,000 per tax year across all your ISAs combined.
There are several types of ISA — cash ISAs, stocks and shares ISAs, innovative finance ISAs, and Lifetime ISAs. This calculator works for any of them: enter your expected annual return and it will project compound growth over your chosen time horizon.
Compound interest means you earn returns on your returns, not just on your original contributions. In the early years, most of your ISA value comes from what you put in. Over time, the growth component accelerates and can eventually exceed your total contributions.
For example, contributing £10,000 per year at 5% growth for 20 years gives you roughly £347,000 — but you only contributed £200,000. The remaining £147,000 is compound growth, and because it is inside an ISA, you keep all of it tax-free.
The growth rate you enter should reflect the type of ISA and the assets held inside it. Cash ISA rates are set by the provider and change over time. Stocks and shares ISA returns depend on the investments you choose and are not guaranteed — the value of investments can go down as well as up.
Try different growth rates in the calculator to see how they affect the projection. This calculator does not adjust for inflation, so keep that in mind when interpreting longer time horizons.
The annual ISA allowance for the 2025/26 tax year is £20,000. You can split this across different types of ISA however you like, but the total across all ISAs cannot exceed £20,000 in a single tax year. The tax year runs from 6 April to 5 April.
Unused ISA allowance does not carry forward — if you do not use it, you lose it. However, money already inside an ISA stays sheltered indefinitely regardless of how large the pot grows. There is no lifetime cap on ISA holdings.
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