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Due date and gestational age from LMP (Naegele)

Also called EDD calculator, Naegele rule, expected date of delivery, POG calculator, period of gestation

Expected date of delivery (LMP + 280 days) and, if you enter a second date, the gestational age on that date.

Fill 3 more fields to see the result.

Formula and scoring

EDD = LMP + 280 days. Gestational age = date − LMP, in completed weeks + days. Dates are handled as calendar days in UTC.

Exam and ward pearls

  • Naegele's rule by hand: LMP + 9 months + 7 days (or − 3 months + 7 days + 1 year) — the same as adding 280 days in most months.
  • A first-trimester CRL scan is more accurate than LMP; ACOG Committee Opinion 700 says a pregnancy without an ultrasound before 22 0/7 weeks confirming or revising the EDD is suboptimally dated.

When not to rely on it

  • Assumes a regular 28-day cycle with ovulation around day 14; no cycle-length correction is applied here.
  • Unreliable with an uncertain LMP, irregular cycles, recent hormonal contraception or breastfeeding, or conception soon after a pregnancy.

Source

  1. Committee Opinion No 700: Methods for estimating the due date. Obstet Gynecol. 2017;129(5):e150-e154. doi:10.1097/AOG.0000000000002046 · PMID 28426621
  2. Johnsen SL, Wilsgaard T, Rasmussen S, Hanson MA, Godfrey KM, Kiserud T. Fetal size in the second trimester is associated with the duration of pregnancy, small fetuses having longer pregnancies. BMC Pregnancy Childbirth. 2008;8:25 (Nägele 40 weeks from LMP; WHO 280 days). doi:10.1186/1471-2393-8-25 · PMID 18627638
  3. World Health Organization. Robson Classification: Implementation Manual. Geneva: WHO; 2017 (term = 37 weeks or more; preterm = less than 37 weeks). Link

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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