Compound Interest Calculator
Project how your savings or investments grow over time with compound interest.
About this tool
Compound interest is the process of earning interest on both your original deposit and the interest it has already generated. Over long periods this snowball effect can turn modest, consistent contributions into a substantial balance, which is why it is often described as the most powerful force in personal finance.
This calculator compounds monthly and assumes contributions are made at the end of each month. Use it to compare scenarios: a higher contribution, a better rate, or simply more time. Small changes to any of the three inputs can produce dramatically different outcomes over a decade or more.
Frequently asked questions
How is compound interest different from simple interest?
Simple interest is paid only on the original principal. Compound interest is paid on the principal plus all previously earned interest, so the balance grows faster over time.
How often does this calculator compound?
It compounds monthly, which closely matches how most savings accounts and index fund returns are modeled.