I'm trying to think of other factors that would affect the mileage you should get. If your MPG fluctuates that would have an affect. Other than that, it could just be that the system that estimates for you is not very accurate.
Maybe the computer calculates based on the vehicles average MPG instead of just your trip's. These could be quite different.
Maybe the computer calculates based on the vehicles average MPG instead of just your trip's. These could be quite different.