Negative Equity Trade-In Auto Loan Calculator

Every number on this page comes from five short steps. There is no hidden markup and no estimate of your credit. Everything you see is the arithmetic below, run in your browser as you type.

Step 1: Find your equity

equity = trade-in value − payoff amount

If the result is below zero, you have negative equity (you are "underwater"): the car is worth less than you owe. If it is above zero, you have positive equity, which works like extra down payment.

Step 2: Work out sales tax

sales tax = (new car price − trade-in value) × sales tax rate

Most states only tax the difference between the new car's price and your trade-in credit, so that is what we use. A few states tax the full price or limit the credit. If yours does, enter an effective rate instead: your expected tax in dollars divided by (price − trade-in). If the trade-in is worth more than the new car, the taxable amount is zero.

Step 3: Add up what you borrow

amount financed = new car price + sales tax + negative equity − down payment

This is the same as price + tax + payoff − trade-in − down payment. Rolling negative equity over means the dealer pays off your old lender and adds that shortfall to the new loan. With positive equity, the same formula subtracts it instead. The result can never go below zero. Your down payment lowers the whole loan; it is not earmarked for the old debt, so "negative equity rolled over" always shows the full shortfall.

Step 4: Turn the loan into a monthly payment

r = APR ÷ 12 ÷ 100
payment = amount financed × r ÷ (1 − (1 + r)^−months)

This is the standard amortization formula used by banks: a fixed payment every month, where early payments are mostly interest and later payments are mostly principal. If your rate is 0%, the payment is simply the amount financed divided by the number of months.

Step 5: Total up the interest

total interest = payment × months − amount financed

Because interest grows in proportion to how much you borrow, the share of your loan that is old debt is also its share of the interest. We show that as total interest × (negative equity ÷ amount financed): the interest you pay just to carry the previous car's balance.

Worked example 1: rolling over $3,000

You owe $18,000 on a car the dealer values at $15,000, and you want a $35,000 car with $2,000 down, 6% sales tax, and a 7% APR over 60 months.

Choosing 84 months for the same loan lowers the payment to $561.45, but total interest rises to $9,962. That is why the calculator shows interest next to the payment.

Worked example 2: positive equity instead

Now suppose you owe only $12,000 on the same $15,000 trade-in, so you have $3,000 of positive equity. Everything else stays the same. The equity works like extra down payment: $35,000 + $1,200 tax − $3,000 equity − $2,000 down = $31,200 financed, a payment of $617.80 and total interest of $5,868. Compared with example 1, the same car and the same down payment finance $6,000 less, and the monthly payment is $118.81 lower.

Worked example 3: paying the gap with cash

Back to owing $18,000 on the $15,000 car. If you add $3,000 of cash to your $2,000 down payment, the negative equity is covered at the dealership instead of financed. The amount financed becomes $34,200 instead of $37,200, the payment falls from $736.60 to $677.20, and total interest drops from $6,996 to $6,432, a saving of $564. That saving is the interest you avoid paying on the old car's debt for five years.

What is not included

Dealer fees, title and registration, add-ons such as extended warranties, and GAP insurance are not modelled, so your dealer's quote may differ by some amount. Lenders also set their own limits on how much above a car's value they will finance. Treat the result as a planning number and compare it with a written offer. See our methodology for how every calculator on this site is tested.

Negative equity, also called being "upside down" or "underwater," means you owe more on your car loan than the car is currently worth. If your loan payoff is $18,000 and a dealer would only pay $15,000 for the car, you have $3,000 of negative equity. It happens because new cars typically lose value fastest in their early years, while the loan balance falls slowly. Long loans of 72 or 84 months, small or no down payments, high interest rates, and financing extras like warranties all keep the balance above the car's value for longer.

It becomes a real problem when you want to trade the car in. The $3,000 gap does not go away: the dealer or lender may offer to roll it into the new loan, which the CFPB says makes the new loan more expensive (Should I trade in my car if it's not paid off?). You then pay interest on a car you no longer own, and you start the next loan already underwater. Repeat this a few times and each car begins with a bigger hole. It also matters if the car is totaled or stolen, since standard auto insurance pays only up to the value of the vehicle, not what you still owe. Guaranteed Asset Protection (GAP) is an optional product meant to cover that difference. The CFPB notes that its price varies a lot, that it may not provide value in every case, and that your own auto insurer may offer a policy (What is GAP insurance?).

1. Keep the car and pay the loan down faster

If the car still runs well, the cheapest way out is often to keep driving it. Add even $50 to $100 a month and ask your lender to apply it to principal, not to next month's payment. Because the balance falls faster than the car's value, the gap closes. If your credit has improved or rates have dropped since you signed, ask a credit union or bank about refinancing, but keep the same remaining term so you do not stretch the debt out. Check the new payoff quote regularly and trade only when your payoff is below what the car is worth.

2. Close the gap with cash instead of rolling it over

Paying the shortfall yourself is the only way to avoid financing it. If you have $3,000 of negative equity and can put $3,000 toward the trade, the old debt disappears instead of costing you interest for years. Set the "Down payment" in this calculator to that amount and watch the payment fall. Also get quotes before you trade: selling the car privately, or getting offers from several dealers and online buyers, often brings in more than one trade-in offer, which directly shrinks the gap.

3. If you must trade, borrow less and borrow for less time

If you need a different car now, reduce the damage. Choose a less expensive or reliable used car so the new loan stays small. Pick the shortest term you can afford; the calculator shows how 84 months lowers the payment but adds thousands in interest. Put down as much as you can so you are not underwater on day one, and consider GAP insurance while the loan is above the car's value. Avoid adding extras to the loan, and try the numbers with a few prices here before you step into a dealership.

This is general education, not personal financial advice. For a large decision, compare written offers or speak with a credit union or a nonprofit credit counselor.