Due Date Calculator

The estimated due date (EDD) is the predicted date of a baby's birth, typically calculated as 40 weeks (280 days) from the first day of the last menstrual period (LMP) — known as Naegele's rule. The actual birth normally occurs between 37 and 42 weeks gestation. Only about 4% of babies are born on their exact due date.

1. 1Naegele's rule: EDD = LMP + 280 days (40 weeks)
2. 2Alternatively: EDD = LMP + 9 months + 7 days
3. 3Gestational age is counted from LMP, not conception
4. 4Conception occurs approximately at week 2 of pregnancy
5. 5Trimesters: 1st = weeks 1–12, 2nd = 13–26, 3rd = 27–40