There are several ways to determine the value of your car when trading it in. One option is to use online valuation tools like Kelley Blue Book or Edmunds to get an estimate of your car's value based on its make, model, year, and condition. You can also get an appraisal from a local dealership or car buying service. Keep in mind that the trade-in value will typically be lower than the private sale value, so it's important to do your research and understand what your car is worth before negotiating with the dealer.