Auto Loan & Trade-In Calculator
This computes the monthly payment on a car loan after subtracting your down payment and trade-in value from the vehicle price. Running it before you sit down at a dealership is the single most useful preparation available, because it separates the four numbers a dealer would prefer to discuss as one.
How to use it
- Enter the vehicle price, trade-in value, and down payment.
- Enter the interest rate and term in months.
- Read the monthly payment, financed amount, and total interest.
Four separate negotiations, presented as one
A vehicle purchase involves the selling price, the trade-in value, the financing rate, and any add-on products. Each is independently negotiable and each affects your cost differently.
The traditional dealership worksheet — the four-square — puts purchase price, trade-in, down payment, and monthly payment in four quadrants and works them together while the conversation centres on the monthly payment. The reason that framing favours the seller is that the monthly payment can be held constant while any of the other three moves against you. Extending the term from 60 to 72 months creates room to raise the price by thousands without the payment changing at all.
The defence is to fix each number separately and in writing: agree the out-the-door price of the car before discussing the trade, settle the trade on its own merits, and arrive with a financing pre-approval from your own bank or credit union so the dealer rate has to compete rather than being the only option.
What a longer term actually costs
Stretching the term lowers the payment and raises the total cost, and the increments are larger than the payment change suggests.
On $30,000 financed at 6 percent: 48 months is $705 a month with about $3,800 total interest; 60 months is $580 with about $4,800; 72 months is $497 with about $5,800; 84 months is $438 with about $6,800. Each step down in payment of roughly $60 to $80 costs about $1,000 more in interest.
The larger problem is equity. A new car loses roughly 20 percent of its value in the first year and around 50 percent by year five, while an 84-month loan pays down principal slowly. That combination leaves you underwater — owing more than the car is worth — for the majority of the loan. Being underwater is not merely unpleasant; it means a total loss or an unplanned sale requires cash out of pocket to settle the loan, and it makes trading out of the vehicle impossible without rolling debt forward.
Negative equity on a trade-in
If your trade is worth less than the balance on its loan, the shortfall does not disappear. It is added to the new loan.
Enter the trade-in value as the actual market value, not the payoff amount, and then treat the difference as an increase in the amount financed. Trading a car worth $12,000 with a $17,000 payoff means $5,000 of negative equity added to the new purchase — you are financing part of a vehicle you no longer own.
This compounds across trades. Each round adds the previous shortfall to a new loan on a new depreciating asset, and the balance owed relative to value grows. Breaking the cycle almost always means keeping a vehicle past the point where the loan is paid off, which is the only reliable way back to positive equity.
The add-ons at the end
Extended warranties, gap insurance, paint and fabric protection, and other products are typically presented after the price is agreed, often as a small change to the monthly payment. Financed over the term, a $2,000 package at 6 percent over 60 months adds about $39 a month and roughly $320 in interest.
Some of these have genuine value. Gap insurance is worth considering on a low-down-payment loan precisely because of the underwater problem above, and it is generally much cheaper from your own insurer than from the dealership. Extended warranties are frequently negotiable by 30 percent or more and can usually be purchased later, so there is no reason to decide under time pressure.
At a glance
| Financed amount | Price minus down payment minus trade-in value |
|---|---|
| Excludes | Sales tax, registration, documentation and dealer fees |
| Negative equity | Enter market value, then add the shortfall to price |
| Transmitted | Nothing |
Frequently asked questions
Why should I not negotiate on the monthly payment?
Because the payment can be held constant while the term is extended and the price raised. Settle the out-the-door price, the trade, and the financing separately.
What does an 84-month loan really cost?
On $30,000 at 6 percent, about $6,800 in interest against $3,800 on a 48-month term. It also leaves you owing more than the car is worth for most of the loan.
How do I handle negative equity on my trade?
Enter the trade at market value, then add the shortfall between value and payoff to the vehicle price. That amount is genuinely being financed.
Does this include tax and fees?
No. Sales tax, registration, and documentation fees are added at purchase and are commonly financed, which raises the payment.
Read more
How loans actually work — Why your first payment is almost all interest, and why the term costs more than the rate.