Compound interest calculator
Enter an amount, a rate and the years. Add monthly contributions if you like.
The compound interest formula
For a single amount, the future value is A = P x (1 + r / n)^(n x t), where P is the starting amount, r is the annual rate as a decimal, n is how many times a year interest is added and t is the number of years.
Example: $10,000 at 6% compounded monthly for 10 years is 10,000 x (1 + 0.06 / 12)^120 = $18,193.97. Interest earned: $8,193.97.
| Compounding | Future value | Interest earned |
|---|---|---|
| Annually | $17,908.48 | $7,908.48 |
| Quarterly | $18,140.18 | $8,140.18 |
| Monthly | $18,193.97 | $8,193.97 |
| Daily | $18,220.29 | $8,220.29 |
Time matters more than frequency
Going from annual to daily compounding adds little. Adding years adds a lot. The same $10,000 at 6% becomes $33,102 after 20 years and $60,226 after 30.
Adding contributions
Monthly additions are added to the balance at the end of each month, or at the start if you choose that. For a savings account, see the savings calculator. For the rate, see the APY calculator.
Questions people ask
What is compound interest?
Interest calculated on the starting amount and on the interest already added.
How is compound interest different from simple interest?
Simple interest is earned only on the starting amount. Compound interest also earns on past interest.
How long to double money?
At 6% compounded monthly it takes about 11.6 years. The rule of 72 gives a quick estimate: 72 divided by the rate.
Does daily compounding matter?
A little. At 6% for 10 years, daily instead of annual compounding adds about $312 on $10,000.