The owner's manual clearly defines the electric range figure as an estimate, but the algorithm used must be fairly accurate as the actual mileage tends to be pretty close unless there are major variations - temp, speed, AC/heat, routes, tires, etc. Unless the estimate is unusually high or low I don't pay much attention. My Volt shows 42 mile electric range today - it may actually get 45 or 37, but either way it is not a big issue for me. I drive the car like I would any other car, the range is what it is, and the ICE extends it to whatever I need. The only numbers I really note are energy usage vs. miles, and total KW used at ICE start. They are a better reflection of vehicle operation and health.