About the Auto Loan calculator
A car’s sticker price is only part of the story. This auto loan calculator builds the amount you actually finance from the vehicle price, your trade-in, your down payment, sales tax and title, registration and dealer fees. It then works out the monthly payment for terms from 36 to 84 months.
You see the sales tax, amount financed, total interest, total loan payments and the total cost of the car, plus a chart of where the money goes and a payment schedule. The working shows each step with your numbers.
How to use it
- Enter the Vehicle price you have negotiated.
- Add your Trade-in value and cash Down payment, if any.
- Enter your Sales tax rate and Title, registration & fees.
- Enter the Interest rate (APR) and choose a Loan term in months.
- Read the monthly payment and the total cost of the car.
The formula
Sales tax is applied to the price after the trade-in credit, and the tax and fees are financed:
Sales tax = (price − trade-in) × tax%Amount financed = price − trade-in − down payment + sales tax + fees
The monthly payment then uses the standard loan formula:
M = P × r(1 + r)^n ÷ ((1 + r)^n − 1)
- P — amount financed
- r — monthly rate = APR ÷ 12 ÷ 100
- n — term in months
Total cost of the car = down payment + trade-in + amount financed + total interest
How trade-ins and sales tax interact
In many states you pay sales tax only on the difference between the new car’s price and your trade-in’s value, and this calculator follows that approach. A cash down payment does not reduce the taxable amount; it only reduces what you borrow. Some states tax the full price regardless of a trade-in, so if that applies to you, the tax shown will be a little low.
For a $35,000 car with no trade-in, 7% tax and $600 of fees, the tax is $2,450. After a $4,000 down payment you finance $34,050. At 6.9% for 60 months that is about $672.63 a month and roughly $6,300 of interest.
Choosing a loan term
Longer terms make a car look cheaper each month but cost more overall. An 84-month loan spreads payments across seven years, adds interest and raises the chance you owe more than the car is worth for a long stretch, since cars lose value fastest in the early years.
A common guideline is to keep the term short enough that the loan shrinks at least as fast as the car depreciates. Try 48 and 60 months side by side and compare total interest. If the shorter term’s payment is a stretch, a less expensive car or a bigger down payment usually saves more than a longer loan.
Dealers sometimes quote only the monthly payment. Focusing on the price, the APR and the total cost line here keeps the comparison honest.
Frequently asked questions
Is sales tax included in the car loan?
Yes, in this calculator the sales tax and fees are added to the amount financed, which is how many dealers set up the loan. Paying them in cash lowers the amount financed.
Does a trade-in reduce sales tax?
The calculator taxes only the price minus the trade-in, which matches the rule in many states. Check your state’s rules if you are unsure.
What is the total cost of the car?
It is everything you pay: down payment, trade-in value, the amount financed and all the interest on the loan.
What if my down payment and trade-in cover the whole cost?
Then there is nothing to finance, and the calculator shows a $0 monthly payment.
Last updated October 24, 2026. Results are estimates for education and planning — see our disclaimer.