First let's have a given to keep answers **based purely on numbers**, and away from opinions and advice on practicality:

* I am financially irresponsible
* I will get approved financing
* Most importantly, my financially responsible spouse will approve it!

How do you compute for losses on an upside down trade-in of a car, for purchase of a new car?
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**Current car to trade-in:**

* Total of monthly payments made for 15-months: $8,505
* Down payment made: $4,750
* Trade-in value (estimated based on black book, 24,000 Km): $28,000
* Total obligation (all-in incl. taxes, 5% interest, 84-months): $48,500 [this was 'day 1' total obligation]

**New car to purchase:**

[![enter image description here](https://i.stack.imgur.com/dwfFj.png)](https://i.stack.imgur.com/dwfFj.png)

Basically, I'm thinking like this:

* I "sell" (trade-in) my car to the dealer for $28,000
* However, I still owe the financing company $35,245 (48,500 total obligation, less 8,505 total payments already made, less 4,750 downpayment)
* So $28,000 less $35,245 = ($7,245)

Meaning, trading in my current car, I immediately lose $7,245, not to mention I will start a new 84-month term. Is this correct?