What happens if I owe more on my trade-in than it is worth?

The shortfall is added to the new loan. On the example above, a car worth $14,000 with $18,000 owed leaves $4,000 of negative equity, so a $38,000 car turns into $40,140 financed. You start the new loan already underwater, and most auto loan calculators have no field for this at all.

Does a trade-in reduce sales tax?

In most states yes: tax is charged on the price after the trade-in allowance is subtracted, so a $14,000 trade at 6% saves $840. California does not allow it. Publication 34 is explicit: "If you accept a trade-in on the sale of a vehicle, the allowance for the trade-in cannot be excluded from the amount on which tax is based." Michigan allows it up to $12,000 in 2026, a cap that has been rising $1,000 a year.

Is the sales tax credit based on what I owe or what the car is worth?

What it is worth. The allowance the dealer gives is what comes off the taxable price, regardless of your loan balance. This is why negative equity costs you on the loan side but not on the tax side.

Why is a 72-month loan a worse deal than the payment suggests?

Because the car depreciates faster than the loan amortises. The payment falls roughly 30% going from 48 to 72 months, the interest roughly doubles, and you spend far longer owing more than the car is worth, which is exactly the position that creates negative equity on the next trade.

Auto Loan Calculator

With vehicle price 38000 usd, trade-in value 14000 usd, still owed on the trade-in 18000 usd, cash down payment 4000 usd and 5 more fields, auto loan comes to $688.21 — monthly payment. It is reached in 14 steps, the last of which is 40140 * 0.006 / (1 - pow(1 + 0.006, -72)), and each one is printed on the page with its numbers filled in. The formula is the one published by California Dept. of Tax and Fee Administration, Publication 34, not an approximation fitted to it.

Car payment including sales tax, fees, and a trade-in — with the negative equity most calculators quietly leave out.

Formula and sources checked 30 August 2026 · How we check

Vehicle price 38000, Trade-in value 14000, Still owed on the trade-in 18000, Cash down payment 4000

$688.21

Monthly payment for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.

It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.

Vehicle priceusdTrade-in valueusdWhat the dealer allows for your old car.Still owed on the trade-inusdOwe more than it is worth? The difference rolls into the new loan.Cash down paymentusdSales tax rate%Trade-in against sales taxMost states tax the price after the trade-in is subtracted. Some do not.Title, registration and dealer feesusdManufacturer rebateusdCash back from the maker. It comes off what you finance, but most states tax the price before it is applied — so it saves less than it looks.Annual interest rate (APR)%Termyears

Monthly payment

$688.21

Equity in the trade-in: 14000 - 18000-4,000
Negative equity rolled into the new loan: max(0, 18000 - 14000)4,000
Trade-in credited against tax: 0 * 0 + 1 * 14000 + 0 * min(14000, 12000)14,000
Amount subject to sales tax: max(0, 38000 - 14000)24,000
Sales tax: 24000 * 6 / 1001,440
Sales tax the trade-in saved: 14000 * 6 / 100840
Out-the-door price: 38000 + 1440 + 70040,140
Amount financed: max(0, 40140 - 4000 - -4000 - 0)40,140
Monthly payment: 40140 * 0.006 / (1 - pow(1 + 0.006, -72))688.209
Total interest: 688.20856 * 72 - 40140$9,411
Total you pay, cash and loan: 4000 + 688.20856 * 7253,551.016
Loan against vehicle price at signing: 40140 / 38000 * 100105.632 %
Paying cash instead, all in: max(0, 40140 - -4000 - 0)$44,140
What financing adds over paying cash: 53551.016 - 44140$9,411

Ask about this in the chat Compare: 72 months against 48 Car Loan Payment by Term Chart

What the loan is made of

Financed$40.1K81%Interest$9.4K19%

Worked example

A $38,000 car, $4,000 down, trading a car worth $14,000 with $18,000 still owed. The $4,000 shortfall rolls in, so you finance $40,140 on a $38,000 car and pay $688.21 a month, a loan worth 105.6% of the car on day one. The trade-in still saves $840 in sales tax, because the credit is based on what the car is worth, not on what you owe.

How to work it out yourself

1.Enter the price you agreed, not the sticker. Then the trade-in allowance and, separately, what you still owe on it.
2.Set how your state treats the trade-in. Most credit it in full against the taxable price; California credits none of it; Michigan caps the credit.
3.Add tax, title, registration and dealer fees to get the out-the-door price. That, less cash down and less trade-in equity, is what you actually finance.
4.Check the loan-to-price line. Above 100% you are financing more than the car is worth on day one, before it depreciates.

Payment and interest by loan term

Payment and interest by loan term
Term (years)	Monthly payment	Total interest	Loan against vehicle price at signing
3	$1,243.08	$4,611	105.63 %
4	$964.93	$6,177	105.63 %
5	$798.61	$7,777	105.63 %
6	$688.21	$9,411	105.63 %
7	$609.75	$11,079	105.63 %
8	$551.26	$12,781	105.63 %

The payment falls with every year added and the interest climbs. The last column is what you owe against the car on day one.

The formula

Equity in the trade-in14000 - 18000
Negative equity rolled into the new loanmax(0, 18000 - 14000)
Trade-in credited against tax0 * 0 + 1 * 14000 + 0 * min(14000, 12000)
Amount subject to sales taxmax(0, 38000 - 14000)
Sales tax24000 * 6 / 100
Sales tax the trade-in saved14000 * 6 / 100
Out-the-door price38000 + 1440 + 700
Amount financedmax(0, 40140 - 4000 - -4000 - 0)
Monthly payment40140 * 0.006 / (1 - pow(1 + 0.006, -72))
Total interest688.20856 * 72 - 40140
Total you pay, cash and loan4000 + 688.20856 * 72
Loan against vehicle price at signing40140 / 38000 * 100
Paying cash instead, all inmax(0, 40140 - -4000 - 0)
What financing adds over paying cash53551.016 - 44140

Source: California Dept. of Tax and Fee Administration, Publication 34 — Motor Vehicle Dealers (trade-ins), Michigan Secretary of State — vehicle trade-in sales tax credit, US Consumer Financial Protection Bureau — auto loans

Questions people actually ask

What happens if I owe more on my trade-in than it is worth?: The shortfall is added to the new loan. On the example above, a car worth $14,000 with $18,000 owed leaves $4,000 of negative equity, so a $38,000 car turns into $40,140 financed. You start the new loan already underwater, and most auto loan calculators have no field for this at all.
Does a trade-in reduce sales tax?: In most states yes: tax is charged on the price after the trade-in allowance is subtracted, so a $14,000 trade at 6% saves $840. California does not allow it. Publication 34 is explicit: "If you accept a trade-in on the sale of a vehicle, the allowance for the trade-in cannot be excluded from the amount on which tax is based." Michigan allows it up to $12,000 in 2026, a cap that has been rising $1,000 a year.
Is the sales tax credit based on what I owe or what the car is worth?: What it is worth. The allowance the dealer gives is what comes off the taxable price, regardless of your loan balance. This is why negative equity costs you on the loan side but not on the tax side.
Why is a 72-month loan a worse deal than the payment suggests?: Because the car depreciates faster than the loan amortises. The payment falls roughly 30% going from 48 to 72 months, the interest roughly doubles, and you spend far longer owing more than the car is worth, which is exactly the position that creates negative equity on the next trade.

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