Compound interest
Watch principal and interest split on the chart as you tweak the numbers.
100% in browser — No files or data are sent to a server. Everything runs on your device.
Calculate the future value of an investment with an initial amount, monthly contributions, annual rate and term. The simulation compounds monthly — the annual rate is divided by 12, the usual retail-calculator convention.
The stacked chart shows what you put in versus what came from interest over the years. Drag the sliders and the result updates instantly, with no signup.
Everything runs in your browser. No financial data is sent to servers. Use it to explore scenarios; it is not professional advice.
Frequently asked questions
Is the rate equivalent or nominal?
Nominal annual rate divided by 12 — the convention most bank and brokerage simulators use.
Are contributions made at the start or end of the month?
At the end of the month (ordinary annuity), the classic future-value formula with PMT.
Do my numbers leave this device?
No. The calculation stays in your browser.
Is this investment advice?
No. It is an educational estimate without taxes or management fees. You can turn on inflation to see purchasing power.
How is inflation applied?
Future value stays in nominal currency. Purchasing power divides that amount by (1 + inflation)^years. Contributions are not auto-adjusted.