+2. I've had it from 5 to 25mpg but it doesn't bother me either way.
The other day the trip would not indicate any higher than 16.9 mpg, I was crawling through 20 miles of 50mph roadworks on the M1. Thought this can't be right. Reset the trip and it jumped up to 22! Sometimes it can get 'stuck', so don't always trust it!