Current market supply and demandYour current car’s trade-in value could then be applied as credit towards your next car purchase. If you own the car outright (zero loan balance), the trade-in value of your car goes directly toward your next car purchase. (Optional) Spare keys, remotes, and the owner’s manual, because keeping the original accessories could also help improve your car’s trade-in value. If you have negative equity, rolling in your current car’s loan balance into financing your new car’s loan can create long-term financial issues and cost you more over time. When you perform a car trade-in at a dealership, they’ll appraise your car to determine its trade-in value.