Compound Interest Calculator
Watch your money snowball with this compound interest calculator. Enter a starting amount, annual interest rate, compounding frequency and optional monthly contributions to project your savings growth year by year.
How it works
Compound growth follows A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods per year and t the years. Monthly contributions are added each period and earn interest too, using the future value of an annuity formula: PMT × (((1 + i)^N − 1) / i).
Frequently asked questions
What is compound interest?
Interest earned on both your original principal and the accumulated interest from previous periods — your money grows faster over time.
How often should interest compound?
More frequent compounding (daily or monthly) yields slightly more than annual compounding at the same nominal rate.
Do regular contributions make a big difference?
Yes. Even small monthly contributions add up dramatically thanks to compounding — try toggling the contribution amount to see.