How is a Due Date Calculated?
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14. For different cycle lengths, the estimated ovulation day is adjusted accordingly.
Due Date = LMP + 280 days (40 weeks)
Or: LMP + 9 months + 7 days
Or: LMP + 9 months + 7 days
Pregnancy Trimesters
| Trimester | Weeks | Key Developments |
|---|---|---|
| First Trimester | Weeks 1–13 | Organ formation, heartbeat detected (~week 6), nausea common |
| Second Trimester | Weeks 14–26 | Baby moves, gender visible, energy typically returns |
| Third Trimester | Weeks 27–40 | Rapid growth, lung maturation, preparation for birth |
Important Notes
- Only 5% of babies are born exactly on their due date — most arrive within 1–2 weeks
- A pregnancy is considered full-term from 39 to 40 weeks 6 days
- Always confirm your due date with ultrasound measurements from your healthcare provider
- A "normal" pregnancy ranges from 37 weeks (early term) to 42 weeks (late term)