Calculate interest on your money over time.
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Enter your values and select Calculate.
Estimate from stated assumptions, not personal financial advice. Rates, fees, tax and account rules may change actual interest. Calculator disclaimer.
How compound interest works
Compound interest earns interest on your savings and on earlier interest. Regular deposits add to the balance earning interest.
Formula & worked example
GBP 10,000 at 5% nominal interest compounded yearly becomes GBP 10,500.00 after one year: GBP 500.00 interest.
With deposits, each deposit earns interest from its selected start or end time. In a partial final period, a start deposit is included when that period begins; an end deposit requires a completed period.
The annual rate uses a 365-day model year: a week is 7 days, and a month is 1/12 of a year. Weekly compounding happens every 7 days; monthly compounding uses equal months. So 52 weeks is 364 days. Partial periods use the equivalent fractional growth factor. Choose Days and daily compounding for a duration measured in days.
Rates & assumptions
A nominal rate is divided by the compounding frequency. APY/AER is an effective annual yield that already includes compounding; the calculator converts it to the equivalent periodic rate.
The model uses equal periods and a constant, non-negative rate. It does not model fluctuating investment returns or market losses.
Fees, tax, inflation, rate changes and bank crediting rules are excluded. Currency changes formatting only, with no exchange conversion. Results are estimates, not guaranteed returns or personal financial advice. Full disclaimer.
Privacy
With JavaScript, calculations run in browser memory. Without it, the native form sends values to Cloudflare for a temporary calculation. Values stay out of URLs and are not saved in a database, analytics or advertising. Server results are private, not cached or indexed.
Normal hosting requests still occur. This public page is configured for Google AdSense. Google and its advertising partners may use cookies and process request information for eligible advertisements, subject to applicable consent choices. This app does not send calculation inputs or results as ad targeting. Privacy policy. Privacy choices. The moon saves only your theme preference in this browser when storage is available. Without JavaScript, the theme applies to the current page.
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Contact & references
Made by IT1ST. Report errors to compound_interest_calculator@it1st.com using example values, without private account details.
References: CFPB annual percentage yield formula and interest accrual and compounding. Check your provider’s terms for its specific convention.