8 Weeks or a Month?

I am so confused! In infants, do you say they are two months old on the "anniversary" of their birthday (the actual date), or do you go by the actual weeks, which would be 8 weeks? 

Technically, not every month has the same amount of days. That being said, the actual date could be off by a few days, depending on the month. 8 weeks is exactly a month, yet today is the 5th. Layna was born on the 8th. So is she two months old today, or just 8 weeks? 

The doctor's office says she can't get her two month shots till after the 8th. An app that I have that tracks the days and weeks tells me 2 months today. 

Soooooo......which is it? Does it really matter? 

In lieu of not really knowing, I took a picture or two today, just with my cell phone, for the two month. On Saturday, the 8th, I'll take more, with my camera. That way I'll have both. 

Here is tonight's, as well as a collage of the ones I took trying to get her settled down. Yet again, she was grumpy. Go fig!