Pregnancy Week Calculator

Count the weeks from the first day of your last menstrual period (LMP) to today. This is your gestational age. A pregnancy at 'week 12' means 12 weeks have passed since your LMP.

Medical convention dates pregnancy from the LMP because it's a known date, while conception date is often uncertain. This means you're technically '2 weeks pregnant' at the time of conception — those first 2 weeks are before the egg was even fertilized.

First trimester: weeks 1-12, Second trimester: weeks 13-27, Third trimester: weeks 28-40. Each trimester lasts about 13-14 weeks and represents a distinct phase of fetal development.