By LMP
By conception
By ultrasound
About Naegele's rule
- Due date = first day of LMP + 280 days (40 weeks)
- Quick math: LMP month + 9 (or − 3), day + 7
- Assumes a regular 28-day cycle; longer cycles push the date back, shorter cycles forward
- Only about 5% of babies are born on the exact due date — 37-42 weeks is normal term
Pregnancy milestones
- Week 6: cardiac activity visible on ultrasound
- Week 12: NT scan / first trimester screening
- Week 16-20: feel first fetal movements
- Week 20-24: anatomy ultrasound
- Week 28: third trimester begins
- Week 37: full term — labor can start any day
- Week 42: post-term, medical induction usually advised