Compound Interest Calculator UK
See how savings grow with compound interest and regular contributions.
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Year-by-year growth
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How it works
Compound interest earns returns on both your original money and the returns already added. Adding a regular monthly contribution accelerates growth further over time.
A = P(1 + r/n)^(nt) + contributions compounded monthly- Longer time horizons benefit most from compounding
- More frequent compounding gives slightly higher growth
- The donut shows how much of your final balance is interest vs money you put in.
Compound interest guides
Frequently asked questions
What is compound interest?
Interest paid on your original savings plus the interest already earned, so the balance grows on an accelerating curve over time.
What is the compound interest formula?
A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the compounds per year and t the number of years.
How much does £5,000 grow at 5%?
Compounded annually for 10 years it grows to about £8,144, earning more than £3,000 in interest.
Is savings interest taxed in the UK?
Interest above your Personal Savings Allowance can be taxable, but interest within a Cash or Stocks & Shares ISA is free of UK tax.
What is the ISA allowance?
You can pay up to £20,000 a year into ISAs, where interest and investment growth are sheltered from UK Income and Capital Gains Tax.
Why does starting early matter?
More time means more compounding, so early and regular saving lets interest build on itself for longer, often beating larger late deposits.
How compound interest grows your savings
Compound interest pays interest on both your original savings and the interest already earned, so a balance grows faster the longer it is left. This calculator projects the future value of a deposit, with optional regular contributions, from the rate and time you enter.
The formula
The core formula is A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the times it compounds per year and t the years. £5,000 at 5% compounded annually for 10 years grows to about £8,144 — over £3,000 of interest.
Tax-free with an ISA
Interest earned in a normal savings account may be taxable above your Personal Savings Allowance, but interest and growth inside a Cash or Stocks & Shares ISA are free of UK tax, up to the £20,000 annual allowance. Over time that tax shelter can make a meaningful difference.
Time is the biggest lever
The longer money compounds, the larger the share of the final pot that comes from interest rather than your deposits. Regular monthly contributions amplify this further, which is why starting early and saving consistently tends to beat larger sums invested later.
Results are estimates for general guidance in United Kingdom and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.