How to Calculate Your Pregnancy Due Date
Your estimated due date (EDD) is calculated as 280 days (40 weeks) from the first day of your last menstrual period (LMP). This is known as Naegele's Rule, the medically accepted standard used by obstetricians worldwide. The assumption is that ovulation and conception occur around day 14 of a 28-day cycle — if your cycle differs, the date is adjusted accordingly.
Our calculator supports three calculation methods: LMP (most common), conception date (if you know when you ovulated), and IVF transfer date (Day 3 or Day 5 embryo).
Pregnancy Trimester Breakdown
| Trimester | Weeks | Key Milestones |
|---|---|---|
| First Trimester | Weeks 1–13 | Heartbeat detected (~6 weeks), morning sickness, organ formation, nuchal scan (11–13 weeks) |
| Second Trimester | Weeks 14–27 | Anatomy scan (~20 weeks), baby movements felt, gender reveal possible, glucose test (~24–28 weeks) |
| Third Trimester | Weeks 28–40 | Baby rapid weight gain, Group B strep test (~35–37 weeks), birth preparation, baby fully developed by week 37 |
When Are Babies Actually Born?
Only about 5% of babies are born on their exact due date. Most births occur within a 2-week window before or after the EDD. A pregnancy is considered:
- Early term: 37–38 weeks 6 days
- Full term: 39–40 weeks 6 days
- Late term: 41–41 weeks 6 days
- Post-term: 42 weeks and beyond (induction typically considered)
Remember: every pregnancy is unique. Use this calculator as an estimate and confirm your EDD with your healthcare provider via ultrasound.