Before I started researching pregnancy pre-TTC, I had no concept of how far along someone was if they said it in weeks. I REALLY had no concept that when someone said "I'm nine months pregnant" they might still have a month til their due date.

For instance, I am exactly 4 calendar months from my LMP, or 17 weeks and 2 days. Yet if I go by some weeks-to-months calculators, I'll be at 5 months on Sunday. If I go by another, I'll be 4 months on Sunday.

Which method is normal? Counting months completed (like you would a birthday) or counting the month you are going through (like centuries)?