Compound Interest Calculator
Enter what you have, what you add each month and the rate you expect. See how much your savings could grow, and how much of it is interest.
What we noticed
Year by year
How this calculator works
Compound interest is interest on your money plus the interest it has already earned. Each period, your balance grows by the rate, and then next period the rate applies to the bigger balance.
We work month by month. Your balance grows by the monthly share of the yearly rate, then your monthly savings go in at the end of the month. We show your balance, what you put in, and the interest you earned.
This assumes the same rate every year and does not include tax or fees. Real returns change from year to year, so treat this as an example, not a promise.
The formula
| Growth with no deposits | Start x (1 + rate / times a year) ^ (times a year x years) |
|---|---|
| Monthly deposits | Each deposit grows from the month you make it |
| Rule of 72 | 72 / rate as a number = about years to double |
Sources: Investor.gov: Compound interest, Investor.gov: Compound interest calculator
Frequently asked questions
What is compound interest?
It is interest earned on both your original money and on the interest you have already earned, so your savings grow faster over time.
How often should interest compound?
More often is slightly better, but the rate matters far more than the schedule. Monthly and daily give nearly the same result.
Why does starting early matter?
Because interest earns interest, early money has more time to grow. Waiting 5 years can cost you a large part of your final balance.
Does this include inflation?
Not in the main result. We show a separate line with what your final balance would buy in today's money.
Is the rate guaranteed?
No. A savings account rate can change. Stock returns go up and down. The calculator uses one steady rate to keep it simple.