• Go to the "Home" tab in the bottom bar.
• Swipe left on your home screen dashboard, which shows your current weeks and days pregnant and baby's hand, foot, and body size comparisons.
• From the second page of your dashboard showing your countdown and due date, tap 
• "Change due date" and edit your details.
• Tap "Save" in the top right corne

All four fields in the due date calculator (estimated due date, weeks pregnant, last menstrual period, and date of conception) are connected and take into account 38 weeks of gestation and approximately 2 weeks from your last period until ovulation.