Glow verses other Pregnancy Apps


Glow which has all my temperatures and knows when I ovulated in it says I’m 5 weeks and 3 days but other apps where I just put my last period info in says I’m 5 weeks and 2 days. Which is right? Is Glow using my ovulation to guess better (I had ovulated on the 15 which is a bit early for me) or are the other ones right and Glow is off a day?