Rebuilt vehicles are obviously worth less than a car that has a clean title and has not in an accident serious enough to find it be a total loss. Generally, a vehicle that has a salvage or rebuilt title can be worth thousands of dollars less than one that does not have a this type of title.
Auto and insurance industry sources report that the decrease in value of a vehicle that has a rebuilt or salvage title is typically between 20 percent up to 50 percent depending on the type of vehicle and its age.
So while there is not any specific percent or amount off of actual cash value that all insurance companies use for calculating the value of a rebuilt title car it will be worth less than a car with a clean, clear title. The diminished value of the vehicle, due to the type of title it had, will thus most certainly decrease your settlement amount if you are getting actual cash value a car with a rebuilt title in an auto accident claim.
If there is a specific car you are wanting to know what the rebuilt or salvage value would be versus a car with a clean title you could discuss this issue with a local dealership. A dealer should be able to give you a reasonable idea of the difference in value in the same car, just one with a clean title and another with a rebuilt title.