Percentage of pregnancy

Donald • TTC baby #1. Off BC since July 2014. Cycle irregular

Me and my girlfriend are using this app to help conceive, she came off the pill and has had a very long gap between periods and we are currently at cd37 this time round. The days on the app tell you a percentage of pregnancy but it says on our fertile days that there's a higher cos centre of pregnancy.

We keep knocking back when AF is starting as she hasn't appeared and a HPT came back negative