Glow tells me my periods due

A.S
Hello there, 
I have been using glow to keep a track of my periods and to monitor my fertile period.
Here is the thing - last 3 months glow predicts my flow on a certain day. But I notice my periods are always later than what is predicted. 
This month too it predicted I would have aunt flow visit me on 23. But no flow. Should I get a Prego test? Or is it too early?