Help with estimated due date

Michelle • Mother to a beautiful baby girl, and a proud step mother to a loving little boy! 👨‍👩‍👧‍👦

I use two apps; Glow and Ava. Ava says I am 4 weeks 6 days and Glow says im 3 weeks 6 days. Why is that? The first day of my menstrual cycle is the same on each app! 🤔🤔🤔