Difference between Glow and Glow Nurture

Hillary

I notice a difference between Glow and Glow <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">Nurture</a> with how far along I am in my pregnancy. My LMP was October 15. Regular Glow says I’m 5 weeks and 2 days while this app says I’m 4 weeks and 6 days. Why the different predictions?