ISA Savings Calculator
Money in an ISA grows free of income tax and capital gains tax, and there is no Personal Savings Allowance limit to worry about.
Enter your current ISA balance, monthly contributions and expected interest rate to see where you could be.
How the calculation works
We believe numbers should be transparent. Here is the formula behind this calculator.
Worked example
Worked example: £5,000 in, £250/month for 10 years
Important assumptions
- Contributions are assumed to stay within the £20,000 annual ISA allowance.
- The interest rate is assumed to stay constant for the whole period.
- A Cash ISA pays interest; a Stocks & Shares ISA grows with investment returns, which can go down as well as up.
Rates & official sources
Every calculation is based on the official rates and rules published by GOV.UK and HMRC.
Frequently asked questions
What is the ISA allowance?
You can pay in up to £20,000 per tax year across cash and stocks & shares ISAs combined. You cannot carry unused allowance forward, so it is use it or lose it each year.
Cash ISA or Stocks & Shares ISA?
Cash ISAs suit short-term savings and money you cannot afford to lose. Stocks & Shares ISAs typically deliver higher long-run returns but you can get back less than you put in.
Is ISA interest really tax-free?
Yes — all growth inside an ISA is free of income tax and capital gains tax. It is the tax shelter that makes ISAs so popular for longer-term savings.
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View calculatorRelated guides
New to the topic? Read a plain-English guide on savings & investments, with worked examples and tips.
How compound interest works
The eighth wonder of the world, with real numbers.
Read the guide Personal FinanceHow much should I save?
A realistic savings target for your income and goals.
Read the guide Personal FinanceBuilding an emergency fund
Three to six months of costs — and how to get there.
Read the guide TaxCapital Gains Tax explained
How Capital Gains Tax works — the £3,000 allowance, the 18% and 24% rates, and when you pay it.
Read the guide TaxSavings interest tax explained
The Personal Savings Allowance and tax on savings interest — £1,000 for basic-rate, £500 for higher-rate, and what happens above.
Read the guideThese calculations are estimates for guidance only and are not professional financial, tax or legal advice. UK rates and rules change, so always verify important figures with official GOV.UK / HMRC information or speak to a qualified professional. See our full disclaimer.