ISA Calculator UK — Grow Your Money Tax-Free
Calculate returns on your Individual Savings Account. Compare Cash ISA Stocks and Shares ISA and Lifetime ISA growth over time with zero tax on gains.
Individual Savings Accounts are the UK equivalent of tax-advantaged investment accounts. The annual ISA allowance is £20000 and all returns whether interest dividends or capital gains are completely tax-free. A Stocks and Shares ISA invested in index funds has historically returned 8-10% annually compared to 3-5% for Cash ISAs. Over 10-20 years the difference is substantial and the tax-free status makes ISAs one of the best wealth-building tools available to UK residents.
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Key Information
| Parameter | Details |
|---|---|
| Annual ISA Allowance | £20,000 |
| Lifetime ISA Allowance | £4,000/year (25% government bonus) |
| Cash ISA Average Rate | 3.5% - 5% (2026) |
| Stocks & Shares ISA Returns | 8% - 10% historical average |
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Use Calculator NowFrequently Asked Questions
How much will £500 per month ISA grow?
£500 per month in a Stocks and Shares ISA at 8% average returns grows to approximately £91500 in 10 years £295000 in 20 years and £750000 in 30 years. All completely tax-free. The same amount in a Cash ISA at 4% would only reach £73500 in 10 years showing the significant advantage of equity ISAs for long-term savings.
What is a Lifetime ISA?
A Lifetime ISA (LISA) allows savers aged 18-39 to save up to £4000 per year toward their first home or retirement. The government adds a 25% bonus meaning you effectively get £5000 for every £4000 saved. The maximum bonus is £1000 per year. Money can be used for a first property up to £450000 or withdrawn penalty-free at age 60.
Cash ISA vs Stocks and Shares ISA?
Cash ISAs are safer with guaranteed returns but typically lower at 3-5%. Stocks and Shares ISAs offer higher potential returns of 8-10% but with market risk and possible short-term losses. For goals under 5 years use Cash ISAs. For goals 5+ years away Stocks and Shares ISAs have historically outperformed significantly.
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Last updated: 24 March 2026