In my Limited AWD I averaged about 27 MPG on a just-completed 1200 mile trip. The majority of the miles were on the highway in ECO mode, typically going about 75 mph. Winds were light and the terrain was flat, so those factors didn't play a big role in the outcome.
Closer to home, commuting to work and running errands in more stop-and-go driving, I'm averaging about 22 MPG.
On right side of steering wheel, button on top left. symbol on it looks like pages. use the little lever just below that on each page to see what you can learn about MPG, miles traveled, what you want shown on the center of display.
There is all kinds of information
I have found that the on board mileage is about 2 mpg higher when I compare the manual way of calculation. All 6 of my Hyundais have been this way, but my 2016 Mazda Miata is almost always the same when compared. I think Hyundai want’s everyone to believe they are getting good gas mileage.
I drive with a light foot and do not speed or jack rabbit start or stop. According to my mileage readout, I'm averaging 15mpg in the city and 19 on the freeway. And that's an average. This is much lower than the book. Should I take it in and have the gage checked?
Try to compare by checking mileage compared to how much gas you use in the course of several fill ups.
Also do you do a lot of city driving where you set a numerous red lights? that is really bad on mpg