Free Compound Interest Calculator
See how a starting amount and monthly contributions grow over time with compound interest, updated as you type.
Estimates only, not financial advice. Actual returns vary and are not guaranteed.
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Frequently Asked Questions
How does compound interest work?
Compound interest is interest earned on both your original principal and on interest that's already been added to your balance. Each period, interest is calculated on the current balance (not just the starting amount), so growth accelerates over time.
What does compounding frequency mean, and does it matter much?
It's how often interest is calculated and added to your balance — annually, monthly, daily, etc. More frequent compounding produces slightly higher returns for the same stated annual rate, but the difference between monthly and daily compounding is usually small.
How are my monthly contributions factored in?
Each month, your contribution is added to the balance after that month's interest is applied, then it starts earning interest itself the following period. Consistent contributions over time are often what drives most of the growth, not just the interest rate.
Is this a guaranteed rate of return?
No — this calculator assumes a constant annual rate for simplicity. Real investments fluctuate, and this is an estimate for planning purposes only, not financial or investment advice.
Should I use daily or monthly compounding to check my real bank account?
Use whatever compounding frequency your bank or account statement lists — it's usually daily for savings accounts and monthly for many investment accounts. Check your account terms if you're not sure.