What is a Auto Loan?
An auto loan is a secured, amortizing loan: the car is the collateral, and you repay a fixed amount each month that covers interest plus a shrinking slice of the principal. The amount you actually finance isn't just the sticker price — it's the price plus sales tax and dealer fees, minus your down payment and trade-in.
That 'amount financed' is what interest is charged on, which is why rolling taxes and fees into the loan quietly raises your total cost: you pay interest on them for the life of the loan.
Why it matters
Dealers negotiate in monthly payments because a lower payment can hide a longer term and thousands more in interest. A $35,000 car at 6.5% costs about $4,600 in interest over 60 months — but stretch it to 84 months for a smaller payment and the interest climbs sharply while the car keeps depreciating.
Seeing the total interest and out-the-door cost — not just the payment — is what lets you compare offers honestly. Two loans with the same monthly payment can differ by thousands once you account for term length and fees.
What to do next
Get pre-approved by your own bank or credit union before you shop, so you walk in with a rate to beat and can treat dealer financing as just another quote. Negotiate the car's price and the financing separately — never let them be blended into 'what payment are you looking for?'
Then use the scenarios above to test a shorter term, a bigger down payment, or an extra monthly payment. Even a modest extra amount each month can shave months off the loan and keep you from being underwater.
Frequently asked questions
How is a car loan payment calculated?
Your payment uses the standard amortization formula on the amount financed (vehicle price + sales tax + fees − down payment − trade-in): P × [r(1+r)^n] / [(1+r)^n − 1], where r is the monthly APR and n is the number of months. Early payments are mostly interest; later ones are mostly principal.
Does a trade-in reduce my sales tax?
In most U.S. states, yes — sales tax is charged on the price minus your trade-in value, so a trade-in lowers both the amount financed and the tax. A handful of states tax the full price; this calculator uses the common trade-in-credit rule.
Is a longer loan term a good idea?
A longer term (72–84 months) lowers the monthly payment but increases total interest and keeps you 'underwater' — owing more than the car is worth — for longer, because cars depreciate quickly. If you can afford the payment on a 48–60 month term, it usually costs far less overall.
How much should I put down on a car?
A common guideline is 10–20% down on a used car and at least 20% on a new one, enough to offset first-year depreciation so you're not immediately underwater. A larger down payment lowers your payment and total interest and can improve your rate.
Can I pay off my auto loan early?
Usually yes, and it saves interest because auto loans are simple-interest. Check your contract for a prepayment penalty first (rare but possible). Use the extra-payment field to see exactly how much time and interest an extra amount each month saves.
What APR should I expect on an auto loan?
Rates depend heavily on credit score, loan term, and whether the car is new or used. Buyers with strong credit see the lowest rates; longer terms and used cars carry higher ones. Always get pre-approved by your own bank or credit union before the dealership so you have a rate to beat.
Uses the standard amortization formula; sales tax follows the common trade-in-credit rule (tax charged on price − trade-in) (2026).