How compound interest works
With compound interest you earn interest on your interest. Each period, your balance grows, and the next period's interest is calculated on that larger balance. The longer your money compounds and the more often it compounds, the bigger the effect. Adding a regular monthly contribution accelerates this even further.
The power of time
Time is the most powerful ingredient in compounding. Starting a few years earlier — even with smaller amounts — often beats starting later with larger amounts. Try changing the number of years above to see how dramatically the final balance moves.
Frequently asked questions
What is a realistic interest rate to use?
It depends on where your money is. High-yield savings accounts often pay a few percent, while long-term stock market averages have historically been higher but come with risk. Use a rate you can reasonably expect.
Does it include my contributions?
Yes. "Total you put in" is your starting amount plus all monthly contributions. "Total interest earned" is everything above that.
Is my data saved?
No. The calculation runs entirely in your browser. Nothing is uploaded.