Compound interest calculator
See how a starting balance grows when interest earns interest, how long doubling takes, and what regular deposits add.
View yearly schedule
Projections are illustrations based on your inputs, not predictions or advice. Actual returns vary year to year.
How compound interest works
Compound interest means each period's interest is added to your balance, so the next period earns interest on a larger amount. Over short periods the effect is modest. Over decades it dominates: at 7% a year, a balance doubles roughly every 10 years, so 30 years means roughly three doublings, or eight times your starting money.
Compounding frequency matters less than people expect. Moving from annual to monthly compounding at 7% lifts the effective annual yield from 7.00% to about 7.23%. The rate itself and the time you stay invested matter far more.
The classic shortcut is the Rule of 72: divide 72 by the annual rate to estimate doubling time. This calculator shows the exact figure alongside your projection.
Common questions
What is the difference between APR and effective annual yield?
APR is the stated annual rate before compounding. Effective annual yield is what you actually earn after compounding within the year, so it is slightly higher whenever interest compounds more than once a year.
Does this calculator include taxes?
No. Interest is typically taxable in the year it is earned unless held in a tax advantaged account. Your after tax result will be lower and depends on your tax situation.
Is compound interest guaranteed?
Only for products with a fixed rate, like some savings accounts and CDs. Investment returns compound too, but they vary year to year and can be negative.