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UK Compound Interest Calculator

See how your savings grow when interest earns interest. Add a starting amount and monthly deposits, choose how often interest is paid, and see your balance year by year in pounds.

Savings accounts show their rate as AER. Investment returns change every year, so use a cautious long-term average.

More options

For example in line with pay rises.

Used for “today’s money”. Central banks aim for 2%.

Future balance

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    Interest earned

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    In today’s money

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    AER

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    Effective yearly rate

    Money doubles in

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    Without new deposits

    Interest and gains inside an ISA are tax-free. You can pay in up to £20,000 a year across all your ISAs (2026/27).

    Growth over time

    BalanceMoney paid inBalance in today’s money

    Year by year

    YearDepositsInterestTotal paid inTotal interestBalance

    How to use the UK compound interest calculator

    Enter your current savings, how much you’ll pay in each month, quarter or year, the interest rate and how many years you’ll save for. The calculator shows your future balance, the interest earned, the AER and how long it takes your money to double.

    Savings, ISAs and pensions

    Use it for a savings account, a cash or stocks and shares ISA, or a pension. Open More options to raise your payments each year and to allow for inflation: the today’s money figure shows what your savings would be worth at today’s prices. Download the year-by-year table as a CSV file for Excel or Google Sheets.

    Assumptions

    The rate stays the same every year and tax, fees and pension tax relief aren’t included. Savings rates change and investments can fall as well as rise, so treat results as estimates for planning, not financial advice.

    Frequently asked questions

    What is compound interest?

    Compound interest is interest earned on your interest as well as on the money you save. £10,000 at 5% a year grows to £10,500 after one year, and the next year’s interest is worked out on £10,500. After 10 years it reaches £16,288.95, compared with £15,000 with simple interest.

    What is AER?

    AER (Annual Equivalent Rate) shows what you would earn in a year once interest is added and compounded, so accounts that pay monthly and yearly can be compared fairly. 5% paid monthly is an AER of 5.116%.

    Do I pay tax on savings interest?

    The Personal Savings Allowance lets basic-rate taxpayers earn £1,000 of interest a year tax-free and higher-rate taxpayers £500. Interest above that is taxed, and the savings tax rates are due to rise by 2 percentage points from April 2027. Interest inside an ISA is always tax-free.

    How much can I put in an ISA?

    You can pay in up to £20,000 a year across all your ISAs in 2026/27. From April 2027 the cash ISA limit is due to fall to £12,000 for most savers under 65, with the rest of the £20,000 available for stocks and shares ISAs.

    How long does it take to double my money?

    Divide 72 by the yearly rate for a quick estimate (the Rule of 72). At 5% that is about 14.4 years. The exact figure is 14.2 years with yearly compounding and 13.9 years with monthly compounding; the calculator shows it for your rate.

    What rate should I use?

    For savings, use the AER the bank quotes, and remember that variable rates can change. For investments such as a stocks and shares ISA or pension, use a cautious long-term average, as returns rise and fall. Results are estimates, not financial advice.

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