Compound Interest Calculator

Use this free compound interest calculator to see how your savings or investments grow over time. Enter your starting balance, regular contributions, interest rate, and time period to instantly calculate your future balance and total interest earned.

How to use this Compound Interest Calculator

1. Enter your starting balance — the amount you are beginning with today, even if it is zero.
2. Enter your monthly contribution — the amount you plan to add every month. This can also be zero if you are not making regular deposits.
3. Enter the annual interest rate — use your savings account rate, expected investment return, or a conservative estimate like 6–7% for long-term stock market averages.
4. Enter the time period — how many years you want to let the money grow.
5. Select the compound frequency — most savings accounts compound monthly. Investment accounts often compound daily or annually depending on the product.
6. Click Calculate Growth to see your future balance, total contributions, and interest earned broken down year by year.

Frequently asked questions

Q: What is compound interest?
A: Compound interest is interest calculated on both your initial principal and the interest you have already earned. Unlike simple interest which only grows on the original amount, compound interest causes your balance to grow exponentially over time. This is why starting to save early has such a dramatic impact on long-term wealth.

Q: How often does interest compound?
A: The compounding frequency determines how often interest is added to your balance. Daily compounding adds interest every day, monthly adds it once a month, and annually adds it once a year. More frequent compounding results in slightly higher returns. Most high-yield savings accounts compound daily, while many investment accounts compound monthly or annually.

Q: What is the Rule of 72?
A: The Rule of 72 is a quick way to estimate how long it takes to double your money. Simply divide 72 by your annual interest rate. For example, at a 7% annual return, your money doubles roughly every 72 ÷ 7 = 10.3 years. This calculator shows the exact figures, but the Rule of 72 is a useful mental shortcut.

Q: What is a realistic interest rate to use?
A: For savings accounts, current high-yield rates range from 4% to 5%. For long-term stock market investments, a conservative historical average is 6% to 7% after inflation. For planning purposes, it is better to use a conservative rate so you are not disappointed by actual results.

Q: Does compound interest work against you too?
A: Yes — compound interest works the same way on debt. Credit card balances and loans with high interest rates compound against you, which is why carrying a balance can become very expensive very quickly. The same math that builds wealth in savings accounts destroys it in high-interest debt.