To calculate your monthly car payment, follow these steps: Enter Sales Price of the vehicle. Enter the number of months you wish to finance. Enter the interest rate. Enter the total of Down Payment PLUS Trade In Value MINUS Trade In Payoff amount. Click on the "Do the Math" button and the estimated monthly payment will appear. Loan Payment Calculator Sales Price No. of Months Interest Rate Down Payment and Trade In Est. Monthly Payment 48 Months 54 Months 60 Months