Free Auto Loan Calculator
How it works
Enter the vehicle’s price, what you are putting down, your trade-in value, and your local sales tax rate. The calculator works out the tax on the taxable amount, subtracts your down payment and trade-in to get the real loan amount, then applies your APR and term to show the monthly payment and the total cost of the car.
Auto Loan Calculator
Your real monthly car payment — tax, trade-in, and down payment all included.
1 The vehicle & what you pay upfront
2 Loan terms
3 Calculate your payment
🚗 Your auto loan breakdown
The formula
First the out-the-door math: sales tax = (price − trade-in) × tax rate, and loan amount = price + sales tax − down payment − trade-in. The monthly payment then uses the standard loan formula with monthly rate r = APR ÷ 100 ÷ 12 and n = term in months: M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1). If the APR is 0%, the payment is simply P ÷ n. Total interest is the total of all payments minus the loan amount.
Everyday uses
- Dealer reality check: run the exact numbers a salesperson quotes you and see the interest hiding behind a “low monthly payment.”
- Term comparisons: compare 48 versus 72 months — longer terms cut the payment but can add thousands in interest.
- Down payment decisions: see how an extra $2,000 down changes both the monthly payment and the total interest.
- Budget-first shopping: start from the payment you can afford and work backwards to the price range you should be looking at.
Frequently asked questions
Why is tax calculated on price minus trade-in?
In most US states, a trade-in reduces the taxable amount of the new vehicle — you only pay sales tax on the difference. A few states tax the full price or cap the credit, so check your state’s rule if the dealer computes it differently.
Is a longer loan term ever a good idea?
It lowers the monthly payment but raises total interest and keeps you “underwater” (owing more than the car is worth) for longer. If you need 72+ months to afford the payment, the car is probably too expensive — a cheaper car on a shorter term almost always wins.
Does a bigger down payment save money?
Yes, twice over: you borrow less, so every monthly payment is smaller, and you pay less total interest over the life of the loan. It also protects you against owing more than the car is worth as it depreciates.