Le guide ci-dessous n'est pas encore disponible en français et s'affiche en anglais. Le calculateur lui-même est entièrement traduit.
Comment utiliser ce calculateur
- Choose how to calculate: last menstrual period (LMP), conception date, or IVF embryo transfer (day-3 or day-5 embryo).
- Enter the date. For LMP, also enter your average cycle length.
- Review the estimated due date, your current gestational age and upcoming milestones.
Formule
Pregnancy is conventionally dated from the LMP: an average pregnancy is 280 days (40 weeks). Naegele's rule assumes a 28-day cycle, so the due date is adjusted by the difference for longer or shorter cycles. Conception typically occurs about 14 days after the LMP, giving 266 days from conception.
Due date = LMP + 280 days + (cycle length − 28)
Due date = conception + 266 days
IVF: transfer date + 266 − embryo age (3 or 5 days)
Example
- LMP on 1 March, 28-day cycle.
- 1 March + 280 days = 6 December.
- With a 31-day cycle, add 3 days: 9 December.
Questions fréquentes
How accurate is a due date?
Only about 4–5% of babies arrive on their exact due date. Most are born within two weeks either side. An early ultrasound gives the most accurate dating.
What if I don't know the date of my last period?
Your healthcare provider can date the pregnancy with an ultrasound, ideally in the first trimester.
When does each trimester start?
The second trimester starts at 14 weeks and the third at 28 weeks of gestation. A pregnancy is considered full term from 39 weeks 0 days (early term from 37 weeks).