The formula to calculate monthly loan payments (i.e. for fixed-rate mortgage) is $(P r)/(1-(1+r)^{-N})$ where $P$ is the principal, $r$ is the monthly interest rate, and $N$ is the number of monthly payments.
What is the difference between this equation and using the equation for compound interest: Monthly payment = $(P(1+(i/12))^N)/N$ where $P$ is the principal, $N$ is the number of monthly payments, and $i$ is the annual interest rate?
Apologies for the formatting of equations.