Medical calculators

EDD / Gestation

Naegele Rule

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How it is calculated

Naegele rule: LMP plus 280 days. It assumes a regular 28-day cycle with ovulation on day 14, so it is unreliable with irregular cycles, recent hormonal contraception or uncertain dates - first-trimester ultrasound is more accurate: in the UK and much of Europe the 11-14 week scan sets the due date. The US (ACOG) re-dates only if the scan differs by more than 5 days before 9 weeks or 7 days at 9-13+6 weeks.

About

Estimated due date from the last menstrual period. Assumes a regular 28-day cycle; a first-trimester scan takes precedence.

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