Should I roll negative equity into my next car loan?

Rolling negative equity into a new loan is generally not advisable because you start the new loan already underwater. If you owe $5,000 more than the car is worth, adding that to a new $30,000 loan means you owe $35,000 on a $30,000 car on day one. This can trap you in a cycle of negative equity. It is usually better to pay down the difference separately if you can.