While that’s true, and while it’s something I’d definitely recommend for others, I can’t honestly say that’s something I’ve mastered doing myself. To me, not finishing just means I have more work to do when it comes to figuring out how many calories I actually ate. While I could just guesstimate that I had 60% of that blizzard, I find that in practice I’m really not okay with being that wishy-washy with the numbers. The days where I have to just guesstimate kill me inside.
And this situation with the blizzard is something I’ve dealt with. I had a mostly finished blizzard but couldn’t finish it. I had to mark the level of ice cream still remaining, empty the cup, then get weight measurements for the empty cup (c), cup full of water (f), and cup full of water up to the level of remaining ice cream (w) - at which point the total calories eaten were (w-c)/(f-c) * B, where B is the number of calories in the full blizzard. If I could have avoided all of that by finishing the last 28% of that blizzard, you bet I would have.
The worst part is that I know the menu calories aren’t precise at most restaurants, but I still won’t let myself be wishy-washy with them. I actively recognize there’s no point in relying on how many calories Outback Steakhouse says are in a Bloomin’ Onion (1900 btw) when the largest bloomin’ onion I’ve had in the past is close to double the size of the smallest I’ve had. But my entire system relies on precise tracking so I still feel I have to make the effort.
Rounding up to the full amount after eating >85% or so is something I do though. I’m much more okay with it if I know I’m overestimating than if I think I might possibly be underestimating.