chester012

I got a 2018 Lexus ES 300h. In the beginning , the mileage per tank is 630 based on the 'Range' predicted by the computer system. This prediction is getting less every time I refilled the gas. The last time after I filled the full tank, it showed 580. I don't understand why the prediction is getting less. Also, every time I start the car, the prediction for remaining mileage is less than what it showed last time I shut down the engine. For example, I stopped and turned off the engine this morning when the prediction of remaining mileage for the remaining gas is 350. In the afternoon, I started the engine and it showed only 345. It keeps doing this so, even though in the beginning the prediction showed 580 miles to go for the whole tank, it would end up only 450 miles for this odo trip when the gas light on. Is this normal? ..
​​​

lesz

When your car is new, its computer is using some pre-determined default mpg to calculate the remaining range.

However, as you build up a history of actual mpg, the computer will use that and adjust the way the it calculates the remaining range. Eventually, when the computer has acquired a large amount of your driving history, the range number will settle in and not be subject to the wider swings that you see when the car is new.

If you were to disconnect the battery and leave it disconnected for, say, 30 minutes, the computer's history will be lost and, thus, the range number will return to the same default that it had when the car was new, and the process of building history to establish a more accurate range will start from scratch.

GES

What you are experiencing is normal. I have 2013 300h and it does the same thing. lesz explanation is correct. Most likely in your last tank or last few tanks your fuel economy was not as good as previously and the computer made the adjustment.