BabyCenter says I"m at 21 weeks (which I agree with) but then my "What to Expect" app on my phone says that this is the start of my 22 weeks......I'm trying to fill out my "Belly Book" and now I'm wondering if I have my weeks all wrong?  It actually has you start entering info on week 1 but do you think that means the 1st week you know you are pregnant or like technically week 1?  If I wrote in it all wrong I'm going to be so mad!  I"m too OCD for that! haha  Because typical me, I flipped to week 21 and started writing.

I was always confused by that too!  I think it's because techincally you are in your 22 week (exampe 21 weeks and 1 day pregnant). 

Does that make sense?

Yeah I guess that does.  Should I still write in my book that i'm 21 weeks though?

yeah just say you're 21 weeks if thats what you agree with. 

When you are 21 weeks you are starting the 22nd week of pregnancy. Just like with the year we are in the 2000's but in the 21st century. Does that clarify it at all?