How is the pregnancy due date calculated?

Naegele's rule: EDD = LMP + 280 days (40 weeks). This assumes a 28-day cycle with ovulation on day 14. Only ~4% of babies are born exactly on their due date; most arrive within 2 weeks before or after.

When does each trimester start?

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40 (birth).

Pregnancy Due Date Calculator

Calculate your estimated due date (EDD) from your last menstrual period using Naegele's rule.

First day of last menstrual period (LMP)

Estimated Due Date

Mar 22, 2027

Monday, March 22, 2027

Currently

0w 0d

Trimester

1st

Days until EDD

279

Pregnancy milestones

Week	Date	Milestone
Week 4	Jul 13, 2026	Positive pregnancy test typical
Week 6	Jul 27, 2026	Heartbeat detectable by ultrasound
Week 10	Aug 24, 2026	End of embryonic period
Week 12	Sep 7, 2026	End of first trimester
Week 16	Oct 5, 2026	Gender may be visible on ultrasound
Week 20	Nov 2, 2026	Anatomy scan / mid-pregnancy
Week 24	Nov 30, 2026	Viability threshold (24+ weeks)
Week 28	Dec 28, 2026	Start of third trimester
Week 37	Mar 1, 2027	Full-term begins
Week 40	Mar 22, 2027	Due date (EDD)
Week 42	Apr 5, 2027	Post-term — induction typically considered

This uses Naegele's rule: EDD = LMP + 280 days, assuming a 28-day cycle. Your doctor may adjust this based on ultrasound dating.

Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator estimates your Estimated Delivery Date (EDD) using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP).

Naegele's Rule

EDD = LMP + 1 year − 3 months + 7 days (equivalent to +280 days). Assumes a regular 28-day cycle with ovulation on day 14.

Trimesters

First trimester: Weeks 1–12
Second trimester: Weeks 13–27
Third trimester: Weeks 28–40