Estimated Due Date

Naegele's rule, adjusted for cycle length. Enter the first day of the last menstrual period.

First day of last menstrual period (LMP)

Average menstrual cycle length (days)

Leave at 28 if the cycle is average/unknown. Naegele's rule assumes ovulation on day 14 of a 28-day cycle — a longer or shorter cycle shifts the estimate.

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Estimated Due Date

Gestational age today—

Trimester—

Adjusted LMP used—

LMP0%EDD (40w)

For reference and educational use only. Naegele's rule is an estimate, not a guarantee — only about half of women recall LMP precisely, and normal delivery spans 37–42 weeks. A first-trimester ultrasound (ideally before 13w6d) is the most accurate dating method and should be used to confirm or revise this estimate, per ACOG guidance. Not a substitute for clinical judgement.