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Compound Interest Calculator

Enter a starting amount, monthly deposit and rate to see your balance grow.

Estimate for general information only — not financial, tax or legal advice. Always check the official figures (GOV.UK / HMRC) or speak to a qualified adviser before making decisions.

Compound interest is interest earned on your interest — which is why saving early matters so much. This calculator shows the future value of a lump sum plus regular monthly deposits, so you can see exactly how a pot grows over time. Figures are estimates and assume a constant rate; real returns vary.

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Frequently asked questions

How is compound interest calculated?

Your balance grows by the interest rate each period, and the next period earns interest on that larger balance. This tool compounds monthly and adds your regular deposits.

Is a higher rate always better?

A higher rate grows your pot faster, but higher returns usually mean higher risk. Savings accounts are safer; investments carry the risk of losses.