How do insurance companies depreciate cars?

Insurance companies don't depreciate cars directly, cars depreciate themselves. Much like houses, cars can go up and down in value over time. But unlike houses, cars tend to go down in value the older they get and usually will not increase in value unless the owner cutomizes the car themselves considerably. If a car is totalled in the event of a crash, the insurance company usually will give the current market value for your zip code BASED on the condition of the car before it was crashed. This is why whenever you purchase insurance the broker or insurance company will take photos of your car. So in case you have any substantial damage, such as a dented bumper, you will be given the book value of your type of car with a dented bumper in it.