Compound Interest Calculator
See how a balance can grow when interest is added to the principal, with an optional regular deposit.
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%
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Optional. Use 0 if you will not add deposits.
About this calculator
Compound interest earns interest on both the original principal and previously credited interest. Adding regular contributions shows how saving steadily changes the result.
How to calculate
Enter the starting amount, annual rate, time in years, and how often interest compounds. Optionally add a monthly contribution. The calculator returns future value, total contributions, and interest earned.
A = P(1 + r/n)^(n×t)
Monthly deposits are end-of-month and use a monthly rate, even when interest compounds on a different schedule:
FV = A + PMT × (((1 + r/12)^(12×t) − 1) / (r/12))
If the annual rate is 0, future value is the starting amount plus the deposits.
When to use it
- Sketching a savings goal
- Comparing annual vs monthly compounding on the same rate
Examples
$1,000 at 5% for 10 years, compounded monthly
Future value is about $1,647.01 if you make no extra deposits.
$1,000 at 5% compounded annually, no extra deposits
| Years | Balance |
|---|---|
| 1 | $1,050.00 |
| 5 | $1,276.28 |
| 10 | $1,628.89 |
| 20 | $2,653.30 |
FAQ
What compounding frequency should I use?
Use the frequency your account actually uses. Banks often compound daily or monthly. Annual compounding is the simplest comparison baseline.
Are contributions added at the end of each month?
Yes. This calculator treats monthly contributions as end-of-month deposits.