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How to compute for losses in an upside down trade-in of a financed car?
I'm going to ignore your numbers to avoid spending the time to understand them.  I'm just going to go over the basic moving parts of trading an upside down car against another financed car because I think you're conflating price and value.  I'm also going to ignore taxes, and fees, and depreciation. The car has an acquisition cost (price) then it has a value.  You pay the price to obtain this thing, then in the future it is worth what someone else will pay you. When you finance a car you agree to your $10,000 price, then you call up Mr. Bank and agree to pay 10% per year for 5 years on that $10,000.  Mr. Banker wires over $10,000 and you drive home in your car.   Say in a year you want a different car.  This new car has a price of $20,000, and wouldn't you know it they'll even buy your current car from you.  They'll give you $7,000 to trade in your current car. Your current car has a value of $7,000.  You've made 12 payments of $188.71.  Of those payments about $460 was interest, you now owe about $8,195 to Mr. Banker. The new dealership needs to send payment to Mr. Banker to get the title for your current car.  They'll send the $7,000 they agreed to pay for your car.  Then they'll loan you the additional $1,195 ($8,195 owed on the car minus $7,000 trade in value).   Your loan on the new car will be for $21,195, $20,000 for the new car and $1,195 for the amount you still owed on the old car after the dealership paid you $7,000 for your old car. It doesn't matter what your down-payment was on the old car, it doesn't matter what your payment was before, it doesn't matter what you bought your old car for.  All that matters is how much you owe on it today and how much the buyer (the dealership) is willing to pay you for it. How much of this is "loss" is an extremely vague number to derive primarily because your utility of the car has a value.  But it could be argued that the $1,195 added on to your new car loan to pay for the old car is lost.