Obstetrics

EDD and gestational age (Naegele)

Estimate due date and current gestation from the last menstrual period.

Version Naegele's rule

Inputs

Days since first day of last menstrual period(days)

Assumes a regular 28-day cycle; confirm with early ultrasound dating.

Gestational age (weeks+days)

20+0

Approximately 140 days to the estimated due date.

Preterm if delivery occurs now — consider steroids and neonatal input between 24 and 34 weeks.
First-trimester ultrasound dating overrides LMP-based estimates.

Formula

EDD = LMP + 280 days; gestational age = days since LMP

DrZep editorial · 2026

Demo content. Educational decision support only. Verify every dose, citation and recommendation against your national formulary and the primary source before clinical use.