anyone else have this issue

So I was playing with one of my other apps on when I'm due I'm 6 weeks and 5 days with the due date as feb 6,2018 but if I mess with the due dates on the apps to Match how far along I am in weeks and days it comes out to Jan 31,2018 soo hmmm. And the lady's in the front desk don't know anyhrjing really about reading due date so I'm going for Jan 31 anyone else have this issue