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.
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.
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ISA Calculator UK
Understanding Your Investment Returns
This calculator projects your returns using compound interest, where your earnings generate their own earnings over time. The power of compounding means that even small regular investments can grow into substantial wealth over long periods. For example, investing just Rs 5,000 per month at 12% expected returns for 25 years can grow to over Rs 1 crore — of which only Rs 15 lakh is your own money and Rs 85 lakh is compounding returns. The key factors that determine your final corpus are: the amount invested, the rate of return, the duration of investment, and the frequency of compounding.
Important Considerations
Past returns do not guarantee future performance, especially for market-linked instruments like mutual funds and equities. The returns shown are estimates based on the rate you enter. Equity investments carry market risk but have historically delivered 12-15% CAGR over 15+ year periods in India. Fixed income options like PPF (7.1%) and FD (6-7.5%) offer lower but more predictable returns. Diversifying across asset classes — equity, debt, gold, and real estate — reduces overall portfolio risk while optimizing returns for your risk tolerance.
Key Information
| Parameter | Details |
|---|---|
| Annual ISA Allowance | £20000 |
| Lifetime ISA Allowance | £4000/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.
What is compound interest and why does it matter?
Compound interest means you earn interest on your interest, not just your principal. Over long periods, this creates exponential growth — even small regular investments can grow into substantial wealth over 15-25 years.
Should I invest regularly or as a lump sum?
Regular investing (dollar-cost averaging) smooths out market volatility by buying at various price points. Lump sum investing works better if markets are undervalued. For most people, regular monthly investing is simpler and more disciplined.
How much should I invest monthly to reach my goal?
The amount depends on your target, timeline, and expected returns. Use this calculator to model different scenarios. The key factors are starting early, investing consistently, and reinvesting returns.
Are investment returns taxable?
Tax treatment varies by investment type and country. Capital gains, dividends, and interest income may be taxed differently. Consult a tax professional for advice specific to your situation and jurisdiction.
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Last updated: March 2026