Compound Interest Calculator: The Complete Guide
Watch your money grow with the power of compounding. Enter your starting principal, the annual rate, the number of years, and how often interest compounds — add an optional monthly contribution — to see the future value and the interest earned.
Who the Compound Interest Calculator is for
Savers and investors who want to see how compounding frequency, time, and regular deposits multiply their money.
How to use the Compound Interest Calculator
- Type your values into the fields above — pick your currency or units where the calculator offers them.
- Results update automatically as you type; there's no submit button and nothing is sent to a server.
- Adjust any input to compare scenarios, then copy the result with a single click.
How it works
Future value = P × (1 + r/n)^(n·t) for the principal, where r is the annual rate, n is the compounds per year, and t is years. Monthly contributions are grown as an ordinary annuity and added on top.
Features
- Annual to daily compounding
- Optional monthly contributions
- Future value & interest earned
- Any currency
Why compound interest matters
Compound interest earns interest on your interest, so growth accelerates over time — the longer the horizon, the larger the effect. Compounding more frequently (monthly or daily versus annually) and adding regular contributions both increase the final balance. It's the single most important idea in long-term saving and investing.