See how a tax-free ISA builds up over time. Add a starting amount and a monthly payment within the £20,000 annual allowance, and the calculator projects your tax-free pot — every penny of growth shielded from tax.
Tax-free · 2026/27 allowance £20,000
An ISA (Individual Savings Account) is a tax-free wrapper. Any interest, dividends or capital gains earned inside it are completely free of UK Income Tax and Capital Gains Tax — and you never declare them on a tax return. You can pay in up to £20,000 across all your ISAs in the 2026/27 tax year.
The calculator compounds your starting amount and monthly payments at the growth rate you choose. For a Cash ISA the rate is the interest; for a Stocks and Shares ISA it's an assumed average annual return.
| ISA type | What it holds | Allowance |
|---|---|---|
| Cash ISA | Savings, fixed or easy-access | Up to £20,000 |
| Stocks & Shares ISA | Funds, shares, bonds | Up to £20,000 |
| Lifetime ISA | First home / retirement, 25% bonus | Up to £4,000 |
| Innovative Finance ISA | Peer-to-peer lending | Up to £20,000 |
Put in £10,000 and add £300 a month in a Stocks and Shares ISA growing 6% a year for 10 years. You pay in £46,000 in total, and the pot grows to roughly £67,400 — about £21,400 of completely tax-free growth. Outside an ISA that growth could face Income Tax or Capital Gains Tax. Compare with an ordinary savings account or model different compounding with the compound interest calculator.
The total ISA allowance is £20,000 per tax year. You can split it across Cash, Stocks & Shares, Innovative Finance and Lifetime ISAs (up to £4,000 of the £20,000 in a LISA), and all growth is tax-free.
A £20,000 lump sum in a Stocks and Shares ISA growing 6% a year would be worth about £35,820 after 10 years, all tax-free. Topping up the allowance each year compounds the effect.
No. Interest, dividends and capital gains inside an ISA are free of Income Tax and Capital Gains Tax, and you don't declare them on a tax return — that's the whole point of an ISA.
Yes. From 2024 you can pay into multiple ISAs of the same type in one tax year, as long as your total payments across all ISAs stay within the £20,000 allowance.
