Understanding your compound interest result
This calculator separates your starting balance, later deposits and accumulated interest. Use it to explore how time and contributions affect a goal, rather than to choose an investment. Select the currency, rate period, compounding frequency and duration before comparing results. A monthly rate is very different from an annual rate.
Worked example
£5,000 at 7% a year, compounded annually without deposits or withdrawals, becomes approximately £9,836 after ten years, £19,348 after twenty and £38,061 after thirty. The thirty-year gain is about £33,061. These are nominal amounts: they do not show what the money could buy after inflation.
Interpreting the result
For a lump sum, the calculation is starting balance × (1 + annual rate ÷ compounding periods) raised to the number of periods. Contributions and withdrawals add cash flows to that timeline. Changing the timing or frequency changes how long each payment earns interest. Read the yearly breakdown to distinguish new money from returns.
Checks before relying on the numbers
Try reducing the assumed rate, shortening the duration and stopping regular deposits. If you need a particular result to meet an essential bill, a projection does not guarantee that money will be available. The smooth line does not model volatile market returns, investment tax or changing savings rates. Include charges in your assumption when appropriate, without deducting the same fee twice.
Read the compound growth guide →
Personal Fortune · Updated 25 September 2026. Educational illustrations, not personal financial advice. Our approach and corrections.