Compound Interest Calculator
See how a savings account grows with compound interest. Enter your deposit, interest rate and years to watch your money multiply — free, instant results.
About this tool
Compound interest is often called the eighth wonder of the world: your money earns interest, and then that interest earns interest too. Over years and decades, this snowball effect turns modest savings into serious wealth.
Enter your starting amount, annual rate, number of years, and how often interest compounds, and watch the growth - the difference between simple and compound interest will surprise you.
How to use
Type your initial principal, the expected annual interest rate, and how many years the money will grow. Choose the compounding frequency - monthly is typical for savings accounts.
Press Calculate Growth to see the final balance and how much of it is interest earned. Increase the years to see why starting early matters more than starting big.
The math behind it
The formula is A = P(1 + r/n)^(n x t), where P is the principal, r the annual rate, n the number of times interest compounds per year, and t the years.
For example, $10,000 at 7% compounded monthly for 20 years grows to about $40,387 - more than $30,000 of it pure interest.
Frequently asked questions
What is the difference between simple and compound interest?
How often should interest compound?
What is a realistic interest rate to assume?
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