Can the gas mileage of my car be wrong?

I bought a used 2005 Hyundai Elantra about a month ago. It has a 14.5 gallon tank, an automatic transmission, and a 4 cylinder engine. The screen that calculates trip length says that since I filled up my tank a few days ago, I have gone about 105 miles and got 23 miles per gallon. However, I now only have a 1/2 tank of gas left. I just filled up on Sunday.



Calculating this myself, I figured that half the tank (7.25 gallons) times 23 miles per gallon should come to about 166.75 miles. Yet, in reality, divide the 105 miles I actually got by 7.25, and the number is really about 14-15.



For a 4 cylinder engine this is awful. Could the trip calculator be wrong in some way (either with the miles or the MPG?), or maybe are my calculations wrong? Or is there something wrong with the way the car is using gas, maybe?Can the gas mileage of my car be wrong?
Three possible reasons for the miscalculation.



1) You reversed a considerable distance, throwing the things out of whack.



2) You didn't count right.



3) You're trip calculator is broken.Can the gas mileage of my car be wrong?
You cannot estimate the gas mileage. The fuel guage will vary. Fill the tank and record the miles. Later refill the tank and then do the math. I'm surprised you don't get better mileage than the 23. I get better mileage than that with a Chevy V-8.Can the gas mileage of my car be wrong?
dont go by the fuel gauge to check this. heres what you do: top off your tank. reset the tripometer to 0. drive for a few days. refill the tank all the way. check how many miles you drove, and record how many gallons it took to refill the tank. so say you went 150 miles on 15 gallons. so then 150/15 = 10mpg. (thats what im gettin in my truck :-(...). get it? hope this clears things up. if youre still gettin a low number, it could be your driving habits. if you have a lot of hills, youll get worse economy, and if youre a jackrabbit as soon as the light turns green and you got a lead foot, thatll also destroy your mpg rating.