Health & Fitness 2026-05-03 4 min read By Konvertibly Team

Due Date Calculator: Calculating Your Pregnancy Due Date and Milestones

Learn how due dates are calculated from LMP and conception, understand gestational vs embryonic age, and key pregnancy milestones by trimester.

Pregnancy Due Date: How It's Calculated

An estimated due date (EDD) is calculated as 40 weeks (280 days) from the first day of the last menstrual period (LMP). Only about 5% of babies are born on their exact due date, but 80% arrive within two weeks either side.

Naegele's Rule

EDD = First day of LMP + 280 days
    OR
EDD = First day of LMP − 3 months + 7 days + 1 year

Example: LMP 1 January → EDD 8 October

Gestational Age vs Embryonic Age

Gestational age is counted from the LMP and is used clinically — at the time of a positive pregnancy test you are typically already 4 weeks gestational age. Embryonic age counts from conception (approximately 2 weeks later). Doctors always use gestational age.

Key Milestones by Trimester

Week 6: Heartbeat detectable on ultrasound
Week 12: End of first trimester; miscarriage risk drops significantly
Week 20: Anomaly scan (mid-pregnancy ultrasound)
Week 24: Viability threshold
Week 37: Full term begins
Week 40: Due date
Week 42: Post-term; induction typically offered

Calculate your due date: Free Due Date Calculator