My daughter has a 2012 Honda Fit 80k A/T she said she is adding more gas than normal I checked it on the dash and it said 21 mpg that seems awfully low was wondering if anyone knows what could be the problem its running fine nothing seems out of whack THX

 

I go with the spark plug issue. I burned up a coil pack before I figured out a spark plug can "just come out". Once I had a new coil pack and athe spark plug fixed all was good and has stayed that way.

Erbid

 

There are many issues that could cause this. Here are some in no particular order:
Low tire preassure
Heavy driving foot. Jack Rabbit starts with heavy footed stops.
Wheel alignment
Bad ball joints/tie rods
Dirty engine air filter. Might as well check the cabin filter too but that won't help gas mileage.
Worn spark plugs
Etc.

These are just from the top of my head. Start with the easy things and work your way up.