Start with the total amount financed.
A lower monthly payment can be created by stretching the loan over more months. That may help cash flow, but it can also increase the total interest paid and keep you in debt longer.
What to compare
APR
APR is designed to help express the cost of borrowing. Compare it alongside the loan amount, term and total of payments.
Loan term
Longer terms generally reduce the monthly payment but can increase total interest and the chance that you owe more than the vehicle is worth for a longer period.
Down payment
A larger down payment can reduce the amount financed, but do not drain emergency savings solely to hit an arbitrary percentage.
Trade-in value and payoff
Treat the trade and the new purchase as separate calculations. If you owe more than your trade is worth, that negative equity may be rolled into the next loan.
Add-ons
Products added in the finance office can increase the amount financed. Understand the price, coverage, cancellation terms and whether you actually want each item.
When refinancing may be worth reviewing
If your credit profile improved, market rates changed or your original loan was expensive, refinancing can be worth comparing. Review fees, remaining term and total interest — not just the new payment.