I’m a bit confused on the whole “weeks pregnant” calculations. How does it work? Why do they say it’s based on the first day of your last period if the sperm hasn’t even reached the egg yet?

Wouldn’t it be more accurate to go from your fertile week or the day you get a positive OPK?

Sorry if I sound naive. Never really had to think of this kind of thing until now.

Partner and I have been properly TTC since February. I’m on the first day of my new fertile week today and I’m trying to work out if I was to fall pregnant this week if I would be far enough along for a Xmas pregnancy announcement?

Any help?