Compound Interest Calculator

About this tool

Compound interest adds earned interest back to the balance so later interest is charged on a larger amount. Optional monthly contributions are added at the end of each month.

How to use

1. Enter a starting amount, annual rate and number of years.
2. Choose how often interest compounds.
3. Optionally add a monthly contribution.
4. Read future value, interest earned and the year-by-year table.

Formula and methodology

Each month the balance is multiplied by (1 + r/n)^(n/12), then the monthly contribution is added. r is the annual rate as a decimal and n is compounds per year (1, 2, 4, 12 or 365). That monthly factor matches the stated compounding frequency.

Worked example

100,000 at 10% compounded monthly for 10 years with no contributions grows to about 270,704. If you also add 5,000 a month, both the deposits and the interest accumulate.