Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

How to compute for losses in an upside down trade-in of a financed car?
Numbers: Estimate you still owe around 37000 (48500 - 4750, 5% interest, 618 per month payment). Initial price, down payment, payments made - none of these mean anything.  Ask your lender, "What is the payoff of the current loan?" Next, sell or trade the current vehicle. Compare to the amount owed. Any shortfall has to be repaid, out of pocket, or in some cases added to the price of the new car and included in the principal of the new loan.  You cannot calculate how much you still owe the way you have, because it totally ignores interest. Advice on practicality:  Don't do this.  You will be upside down even worse on the new car from the instant you drive off the lot.  Sell the current vehicle, find a way to pay the difference - one that doesn't involve financing. Cut your losses on the upside down vehicle. Then purchase a new vehicle. I'm in the "Pay cash for gently used" school, YMMV. Another option is to go to your bank.  Refinance your car now to get a lower interest rate.  Pay as much of the principal as you can.  Keep that car until it is paid off.  Then you will not be upside down. If you're asking how to use the estimator on the webpage.  Put the payoff in the downpayment as a negative and the trade in value in the trade in spot.  Expect the payment to go up significantly.   Another opinion that might be practical advice.  Nothing we say here will convince your financially responsible spouse that this is a good idea.