I always got confused by this too! Turns out they count from last period not conception, so it shows as 40 weeks. My doctor confirmed my due date at the first scan.
I used a pregnancy app and it counted from my last period date, total 40 weeks which is about 280 days. The app gave me an estimated due date instantly. Pretty handy to track week by week.
Think of it as nine months and a little, the official count is 40 weeks. Dont worry if baby comes a week early or late, anytime around 37-42 weeks is considered fine.
It's roughly 280 days, that's 40 weeks counted from your last period. Comes out to about 9 months plus a bit. Baby can arrive a little before or after, that's normal.