Compound interest calculator
See how money grows when the interest it earns starts earning interest too. Enter a starting amount, what you add each month, a rate and a number of years.
Balance after 20 years
$109,333
- Money you put in
- $58,000
- Interest earned
- $51,333
- Interest as a share of the balance
- 47%
Interest is added monthly at one-twelfth of the yearly rate. Taxes and fees are not subtracted.
Year by year
How compound interest is calculated
Each month the balance is multiplied by one plus the monthly rate, which is the yearly rate divided by 12. Money you add is put in at the end of the month and starts earning from the next one. Over many years most of the balance can be interest, not deposits, which is why the line curves upward.
For retirement planning
The retirement savings calculator does the same arithmetic by age and adds a yearly withdrawal. The 401(k) calculator adds an employer match and the IRS limits.