How to figure erythritol when entering manually

I don’t enter it. 

You hear different things because there are different needs. Some folks can use sugar alcohols, count them zero and lose weight. Some people will stall weight loss eating any at all. And all in between. You can start not counting them and change if your weight loss slows. If I wanted to count half, I would add it as a custom food so I could enter my own figures but I wouldn't check to add it to the database.