- Enter your starting balance, monthly contribution, expected annual return and time horizon.
- The calculator compounds monthly — matching how most savings accounts and index funds actually grow.
- It shows your final balance split into money you contributed versus growth you earned.
- Try doubling the years — growth accelerates over time because you earn interest on your interest.
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Compound Interest Calculator — Watch Your Money Grow
Compound interest is the eighth wonder of the world — see it in action. Enter a starting amount, a monthly contribution and an expected return to see exactly how much your savings grow over time, and how much of the final figure is pure growth.
How the compound interest calculator works
Frequently asked questions
What is compound interest?
Compound interest is interest earned on previously earned interest. Instead of only growing on what you deposit, your balance grows on the full balance, so growth accelerates over time — the reason starting early matters so much.
Is a 7% annual return realistic?
Historically, broad stock-market index funds have averaged around 7% per year after inflation over multi-decade periods, though any single year can be far higher or lower. Savings accounts pay much less but are guaranteed.
Does this work for 401(k) or retirement planning?
Yes — enter your balance as the initial amount and your monthly contribution. Add employer match separately (e.g. if your employer matches 100% up to 5%, double your contribution figure).
What if I only contribute a lump sum?
Set the monthly contribution to 0 and the calculator shows pure lump-sum compounding on your initial amount.
Estimates are for guidance only and are based on published 2025/2026 rates. Always confirm with a qualified professional for financial decisions.