Trading in a car changes your new auto loan in three ways: it lowers the price you finance, it can reduce sales tax in most states, and if you still owe money on the trade, that payoff must be handled. This calculator puts all of it together so you know your real payment before you sit down at the dealership.
How this calculator works
Trade-in equity is the trade's value minus what you still owe. Positive equity works like a down payment. Negative equity — owing more than the car is worth — gets added to your new loan.
Sales tax is calculated on the vehicle price minus the trade-in value, which is how most US states handle it. A handful of states (including California, Michigan in some cases, and Virginia) tax the full price, so set the rate accordingly.
Amount financed = price + tax − equity − cash down. The monthly payment uses the standard amortization formula over your chosen term.
The formula
Financed = Price + Tax − (Trade − Owed) − Down; M = F × r / (1 − (1 + r)^−n)- Tax
- (Price − Trade) × sales tax rate
- F
- amount financed
- r
- monthly rate = APR ÷ 12
- n
- term in months
Worked example
You are buying a $38,000 vehicle and trading in a car worth $12,000 that still has $8,000 owed, so you have $4,000 in equity. You add $3,000 cash.
Sales tax at 6.5% applies to $38,000 − $12,000 = $26,000, giving $1,690. Amount financed = $38,000 + $1,690 − $4,000 − $3,000 = $32,690.
At 7.5% APR for 60 months, the payment is about $655 and total interest is around $6,600. Stretching to 72 months lowers the payment but adds roughly $1,400 more interest.
Tips
- Get a trade-in quote from at least two other buyers before accepting the dealer's number.
- Negotiate the vehicle price and the trade-in separately.
- Avoid rolling negative equity into a long loan — you can stay underwater for years.
Frequently asked questions
Does a trade-in reduce sales tax?
In most US states, yes: sales tax is charged on the price after subtracting the trade-in value. A few states tax the full purchase price. Check your state's department of revenue.
What is negative equity on a car?
Negative equity means you owe more on your loan than the car is worth. When you trade it in, the dealer pays off the old loan and adds the shortfall to your new loan.
Is it better to trade in or sell privately?
Selling privately usually gets a higher price, but trading in is faster and may save sales tax. Compare the private-sale price with the trade offer plus the tax savings.
What is a good car loan term?
Shorter is cheaper. Many financial planners suggest 60 months or less for a new car and 48 months or less for a used car to limit interest and reduce the risk of negative equity.