Prius Prime 2017 not getting 621 miles on gas.

In general, the Prius Prime 2017 is designed such that the fuel gauge will tell you that the car's gas tank is empty when you actually have about 3 gallons of gas left.

 

It's a guess-o-meter based on your driving style.
I'm guessing you rarely plug the car in, you do short hops, your not driving in ECO mode and you've got a low eco score. If your doing short hops, best to run the car in EV mode. I plug-in everyday, drive 50-50 mix of highway/city and I'm getting 1.1K-1.3K per tank. Last calculated fill-up was 112 mpg. Odometer read 119 mpg. The EV usage accounts for a lot of your mpg savings. Your still getting around 40 mpg, I'm assuming your pumping in 11 gallons on a fill-up. What did you get on the last ICE only car you've driven? I bet that car performed below EPA standards too.

On your next fill-up, try dividing the number of gallons you put into the tank by the number of miles you've driven on that tank to get a 'true' reading.

Hope this helps

 

it's not a toyota claim, it's an epa test. if your car is in good condition, it will get that when you run the test. YMMV