Edmunds.com's proprietary pricing system takes into account all market variables and gives you the bottom line price. A vehicle's mileage suggests the amount of wear and tear the vehicle has experienced. The TMV Used Vehicle Appraiser adds or deducts the appropriate amount if the vehicle's mileage is below or above the normal range for a vehicle of that age.
Keep in mind that cars typically have accumulated about 12,000 to 15,000 miles per year. Anything over this mileage reduces the value of the car; anything less increases the car's value.
How to Get a Used Car Bargain
For calculating True Cost to Own, Edmunds uses 15,000 miles a year as the baseline.
So, I think it's safe to say that "normal" annual miles is between 12,000 and 15,000 miles a year. I don't have access to the proprietary formula to peg it any closer than that.