Why does my trip computer show higher mpg than manual calculation?

[AlexanderA]

I’ve been tracking my fuel consumption for a few months now and I’m starting to wonder if my car’s trip computer is being a bit too optimistic with its numbers. When I calculate it manually at the pump, I’m consistently getting about 2 miles per gallon less than what the dashboard display tells me. Has anyone else found this kind of discrepancy with their own vehicle?

[Matthew.J]

Yep, I’ve noticed the same thing. My dash climbs higher than my pump math by a couple mpg after a full tank.

[Natalie30]

I wonder if the trouble is with the display or the numbers you’re pulling from the pump. It wouldn’t surprise me if the car’s calculator is a bit optimistic.

[RobertVG]

I did a little test last month: filled to full, reset the trip, drove normally, then calculated mpg by miles divided by gallons. The dash read higher by about one to two mpg every time. Not sure if it’s calibration, tire size, or something else.

[MatthewZM]

Maybe the real issue isn’t the car at all but how we measure it—rounding, warm engines, or when you reset the counter. It’s easy to drift off topic, but I still keep checking, just in case I’m misunderstanding something.