# Compunding periodic payments

## MrAnchovy

For a series of $n$ periodic payments accumulating interest at a rate of $r$ per period, the total compound interest is $\frac{(1-r^n)}{n(1-r)}-1$.

Note that to convert an annual rate (APR) $r{\tiny APR}$ to a monthly rate use the formula $(1+r{\tiny APR})^\frac{1}{12}-1$.