Compound interest calculator

Enter your figures to see how savings or investments could grow over time. Try changing the number of years or the monthly amount to see how each one affects the result.

Assumes contributions are made at the end of each month. Results are estimates, not financial advice. See our Disclaimer.

  • Does compounding frequency matter? It does, but less than the rate and the time period. Monthly compounding gives a little more than annual at the same rate.

  • Are contributions added at the start or end of the month? The calculator assumes the end. Paying at the start of each month would give slightly more growth.

  • Is the result guaranteed? No. Returns vary, and this tool shows what a fixed rate would produce, not what an investment will earn.

  • Can I use this for a savings account? Yes, with the rate your account pays. Check whether the rate is fixed or variable.

How it works

Interest is added to your balance, and the next period’s interest is calculated on the new, larger total. This is compounding. The calculator applies it to your starting amount and to each monthly contribution, and assumes contributions are made at the end of each month. More frequent compounding gives slightly more growth, all else being equal.

Worked example

$1,000 invested for 10 years at 7%, compounded monthly, with no further contributions, grows to about $2,010. The $1,010 difference is the interest earned. Add $100 a month and the total rises to about $19,300, of which $13,000 is your own payments.

How to read your results

Total contributions is what you paid in, including your starting amount. Total interest earned is the growth on top of that. Future value is the total, and the figure to compare with your goal. The result assumes a fixed rate for the whole period, and real returns usually change, so treat it as a planning estimate.

Frequently asked questions