Pregnancy dates

Expected date of delivery

Add the LMP

LMP, first day

Cycle days

As on

About

EDD = LMP + 280 days + (cycle length − 28)

Naegele's rule. It assumes a regular cycle and a sure LMP; an early ultrasound date takes priority when the two differ.

Trimesters: up to 13 weeks 6 days, 14 to 27 weeks 6 days, 28 weeks onward.