Estimated due date predictions on apps

Kitty • Living with PCOS. Mom of THREE boys Jayden💙Ethan💙 Logan💙
Why do some apps say doctors count from the 1st day of your period and not the last. I was always told it's the last day. Even when I went to urgent care they said it's the last day but I have now 6 <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">pregnancy apps</a>. Just to read articles and see the difference in information given and literally 5 out of the 6 say I'm about 1-2 weeks ahead than what <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">nurture</a>/glow says. I don't know my due date because they want me to wait for a sono due to my irregular periods. But these apps are so confusing....