You need this app! The easiest car loan calculator you'll ever find. This calculator is using the formula below.
(P x (i / 12)) / (1 - (1 + i / 12)-n)
P = Principal (main loan, minus your down payments)
i = APR Interest rate in Percentage %
n = Number of months to pay terms
This application provides the most logical estimate for your loan, this will never report the exact amount due to so many different variables considered, but it will be really close.