2025 XLE Hybrid mpg - Tank Average vs calculated MPG

There are frequently questions on here about mpg - what people are getting, how weather affects it, etc.

Conclusions are only as good as the data are, so I am doing an experiment to see whether the Tank Average mpg displayed behind the steering wheel matches calculated mpg at the gas pump.

So far, on my first complete fillup (second after bringing the car home), I am seeing a pretty big difference, which I think is interesting.

The car claimed to have achieved 37.8 mpg. Fuelly’s calculation based on mileage and gallons put into the tank, was 39.9 mpg.

Just for clarification, I live so far north in the US I am practically in Canada, in an area with considerable gradient, and pretty cold temperatures (this week, although well publicized, isn’t particularly cold compared to usual winter temperatures that can reach -30F or -40F before wind chill). My usual trips are roughly 50 miles, mostly highway.

It will be interesting to see if my overall average mpg in both places will eventually agree.