Determine the loan amount: vehicle price plus taxes, fees, and add-ons minus down payment and trade-in value
Convert the annual interest rate to a monthly interest rate by dividing by 12
Convert the loan term from years to months by multiplying by 12
Use the loan payment formula: Payment = [P × r] / [1 – (1 + r)^-n]
Let P = loan amount, r = monthly interest rate, and n = number of months
Plug the values into the formula to calculate the monthly payment
Add any required monthly costs such as insurance, maintenance, or extended warranty if you want the total monthly car cost