What is the US Auto Loan?
A US auto loan finances the vehicle price plus sales tax and title fees, less your down payment and trade-in. Most states tax only the difference between the price and your trade-in, which makes trading in more valuable than it first appears.
Average new-car loan terms have stretched to 68 months, which lowers payments but leaves many buyers owing more than the car is worth for years.
Formula & worked example
Amount financed = Price + tax + fees − down payment − trade-in
Payment = L × i × (1+i)N / ((1+i)N − 1)
Worked example: a $38,000 vehicle with $5,000 down and an $8,000 trade-in. Sales tax at 6.5% on the $30,000 difference is $1,950, plus $500 in fees — financing $27,450. At 7.25% over 5 years the payment is about $547 with roughly $5,360 of interest.
How to use this us auto loan calculator
- Enter the negotiated price, not MSRP.
- Most states tax price minus trade-in — a real saving worth factoring in.
- Use the APR from your credit union or bank, not just the dealer offer.
- Keep the term at 60 months or less if you can.
Smart tips
- Get pre-approved financing before visiting the dealer; it becomes your negotiating floor.
- Negotiate the vehicle price, not the monthly payment. Payment-focused negotiation hides term extensions.
- Terms beyond 60 months mean you will likely owe more than the car is worth for several years.
- Gap insurance is worth considering if your down payment is under 20%.
- Dealer add-ons — paint protection, extended warranties — carry huge margins and are almost always negotiable or refusable.
Frequently asked questions
How is sales tax calculated on a car with a trade-in?
Most states tax the difference between the purchase price and your trade-in value, which reduces the tax meaningfully.
What is a good auto loan rate?
For strong credit, roughly 5–7% for new and 6–9% for used in 2026. Credit unions frequently beat dealer financing.
Should I take a 72 or 84-month loan?
Generally no. Longer terms lower the payment but you stay underwater longer and pay far more interest.
Is it better to put money down or trade in?
Both reduce the amount financed. A trade-in additionally reduces sales tax in most states, making it slightly more efficient.
Want the theory behind the numbers? Read our car buying guides on the Money Blog.
Written by Gurjeet Singh, Sharpen Solutions. Last reviewed 30 Sep 2026. How we check these numbers.