Compound Interest Calculator
See how a balance grows with compound interest and optional regular contributions.
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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)ⁿᵗ
With deposits: FV = P(1 + r/n)ⁿᵗ + PMT × (((1 + r/n)ⁿᵗ − 1) / (r/n))
Examples
$1,000 at 5% for 10 years, compounded monthly
Future value is about $1,647.01 if you make no extra deposits.
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.