ISA Calculator 2026/27: Project Your Growth
This ISA calculator estimates what your ISA could be worth. Enter a starting balance, your monthly or annual contribution, an expected rate of return, and a time frame, and it projects the tax free value. The 2026/27 ISA allowance is £20,000, and growth inside an ISA is tax free.
Figures verified against Bank of England base rate on .
Written by James HartleyCIMA
Calculator
Illustrative assumption only (default 5%). Cash ISAs: lower; Stocks and Shares: variable.
Projected ISA value after 10 years
£31,186
Tax free inside an ISA wrapper
Total contributions
£24,000
Total growth
£7,186
Effective annual saving
£2,400
Year-by-year breakdown▼
| Year | Contributions | Growth | ISA value |
|---|---|---|---|
| Year 1 | £2,400 | £66 | £2,466 |
| Year 2 | £4,800 | £258 | £5,058 |
| Year 3 | £7,200 | £583 | £7,783 |
| Year 4 | £9,600 | £1,047 | £10,647 |
| Year 5 | £12,000 | £1,658 | £13,658 |
| Year 6 | £14,400 | £2,423 | £16,823 |
| Year 7 | £16,800 | £3,349 | £20,149 |
| Year 8 | £19,200 | £4,446 | £23,646 |
| Year 9 | £21,600 | £5,722 | £27,322 |
| Year 10 | £24,000 | £7,186 | £31,186 |
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How this ISA calculator works
Enter your starting balance, contribution amount, and frequency (monthly or annual). Add an expected annual rate of return and the number of years you plan to save or invest. The calculator projects your tax free ISA value using standard future value maths: your lump sum plus each contribution, compounded monthly at one twelfth of your annual rate. Contributions are applied at the start of each month (monthly mode) or once at the start of each year (annual mode).
For the full rules on types, transfers, and the Lifetime ISA, see our ISA guide UK.
The 2026/27 ISA allowance
You can pay up to £20,000 into ISAs in the 2026/27 tax year. That limit is shared across Cash, Stocks and Shares, Innovative Finance, and Lifetime ISAs (the Lifetime ISA has its own £4,000 cap within the total). The allowance resets on 6 April 2026 each year and does not carry over.
Turn on the allowance cap in the calculator if you want annual contributions limited to £20,000 when your entries would exceed HMRC rules.
Cash versus Stocks and Shares returns
A Cash ISA pays interest like a tax free savings account. Rates are typically lower but the balance does not fall with market moves. A Stocks and Shares ISA holds investments such as funds and shares. It aims for higher long term returns, but the value can go down as well as up.
Use a lower rate for Cash ISA projections and a cautious, clearly labelled assumption for Stocks and Shares. Compare the two in our Cash ISA vs Stocks and Shares ISA guide. You can also model general savings with the savings calculator or explore compounding with the compound interest calculator.
Important: returns are not guaranteed
The projected figure assumes your chosen rate stays constant for the whole period. Real Cash ISA rates change when providers reprice accounts. Stocks and Shares ISAs follow markets, so year to year returns vary widely. You may get back less than you pay in. This tool is for planning only, not personal advice.
Example: £0 starting balance plus £200 a month at an illustrative 5% for 10 years projects about £31,186 before fees, with £7,186 of growth.
Frequently Asked Questions
It depends on your contributions, rate of return, and time. Enter your figures above to see a projection. Returns are not guaranteed.
Up to £20,000 in the 2026/27 tax year across all your ISAs.
No. Interest, dividends, and capital gains inside an ISA are tax free.
The calculator compounds your starting balance and contributions at your chosen rate over the time frame you set. Contributions are added at the start of each month or year, and growth compounds monthly at one twelfth of your annual rate.
No. It is an estimate at a fixed rate. Real returns vary and investments can fall as well as rise.
Cash ISAs pay interest and are lower risk. Stocks and Shares ISAs aim for higher returns but can fall in value. See our ISA guide for a comparison of the four ISA types.
Yes, the £20,000 allowance resets on 6 April 2026 and unused allowance is lost.
Use a realistic, clearly labelled assumption. Past performance does not guarantee future returns.
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Related Guides
Cash ISA vs Stocks and Shares ISA: Which Suits You in 2026/27?
Compare risk, returns, access, and how to split your £20,000 allowance.
Read guideISA Guide UK 2026/27: Allowance, Types and Rules Explained
Your £20,000 ISA allowance, the four ISA types, Lifetime ISA rules, and transfers.
Read guideCompound Interest: How to Build Long-Term Wealth in the UK
ISAs, the Rule of 72, and keeping fees low for long-term compounding.
Read guideUK Inflation: How Rising Prices Are Eroding Your Savings
How inflation affects real returns on cash and why tax free wrappers matter.
Read guideWas this calculator helpful?
Official Rates Used
This calculator uses official HMRC rates for 2026/27. View the current rates at GOV.UK:
Rates last verified:
Disclaimer: This calculator provides estimates based on standard HMRC rates for 2026/27. Results may vary based on individual circumstances. This is not financial advice. Always consult a qualified accountant or CIMA-qualified financial adviser for personal tax matters.