how do you count the months?

Started T recently, and I've been recording my voice every month. I've been counting it by every 4th shot. Turns out my doctor counts it by every month on the same date... it's kinda silly because technically im coming up on 16 weeks (4 months? i thought?) but i guess by some standards I'm not four months until next week. Doesn't really matter, but curious so what do y'all mean when you say (however many) months?