I either go for about half and call it good or just round it up to the full amount when counting and then not worry too much if some other things are 5-10% higher than they should be.
It isn’t like the menu calories are precise. Heck, for a blizzard it could be up to 15% more when served if it is above the cup line.
The important thing is paying more attention to what we are eating, how high in calories things are, and whether we actually know what a portion size is.