Due date??

Jamie • Got our BFP on valentines day. Due date Oct. 23
I have a question.... I got a BFP on the 12th of this month. I was curious when my due date was so I got an app and it asked me to plug in the first day of my last period and now it's saying I'm 4 weeks and 3 days is that right? Considering I just got my BFP last week?? My first doc appt is on the 7th of March.