In general you will never see the EPA mileage listed for the car when it was new. You did not reveal whether you have a 4-cylinder or V6 engine or mileage on the vehicle, but either way that mileage sounds too low even for city driving. (Friends with a V6 Sonata averaged about 22 mpg in mixed driving when they had it.)

See the FAQ for general ways to improve gas mileage. Also check codes and a snapshot of live data to look for anything suspicious.

Welcome new member.  I doubt that kind of mileage drop is due to the usual gas mileage things like under inflated tires and that kind of stuff.  Sounds like you have a problem.

First thing is to calculate the real mileage at the gas pump (fill it full, drive most of a tank, refill it, and divide miles by gallons). Next thing is to make sure it’s stock and that the previous owner didn’t add any “performance” parts.  Third, make sure regular maintenance is up to date, particularly oil, filter, and air filter.

If you haven’t found the problem, plug in an OBD scanner and see what codes come up (most auto parts stores will do that for free).  If there are any stored trouble codes, come back and tell us what they are.  Finally, you would need to take it to a mechanic who can look at live data.

PS: the other thing to do is look on Hyundai forums to see if there is a known problem with that model.