Compound Interest Calculator
See how your money can grow through the power of compound interest. Enter your starting balance, contributions, rate, and time to estimate your future balance.
How it works
Compound interest means you earn returns not just on your original deposit, but also on the interest you've already earned. Over time this snowball effect can dramatically grow your savings.
The future value of the initial deposit uses A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounds per year, and t is years. Regular monthly contributions are grown using the future value of an annuity: FV = PMT × ((1 + i)^m − 1) / i, where i is the monthly rate and m is total months.
Tips
Start early — even small amounts compound powerfully over decades. The longer your money stays invested, the larger the interest-on-interest effect becomes.
Increasing your contribution rate and reinvesting all earnings maximizes growth. More frequent compounding (e.g. monthly vs annually) also slightly boosts your returns.
FAQ
What is compound interest?
Compound interest is interest calculated on both your original principal and the accumulated interest from previous periods, allowing your balance to grow faster over time.
Does compounding frequency matter?
Yes. More frequent compounding (daily or monthly vs yearly) produces slightly higher returns because interest is added to your balance more often.
Is this calculator accurate for investments?
It gives a solid estimate using a fixed rate, but real investment returns vary year to year. Use it for planning, not as a guarantee.