Pregnancy Due Date Calculator

Calculate your estimated due date (EDD) from your last menstrual period or conception date.

Calculate from: First Day of Last Period Average Cycle Length

How Is Your Due Date Calculated?

Naegele's Rule (LMP Method)

The standard method adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. For longer or shorter cycles, the calculation adjusts accordingly.

Important: Due Dates Are Estimates

Only about 5% of babies arrive on their exact due date
Full term is defined as 39–40 weeks; 37–38 weeks is "early term"
Term is 37–42 weeks; post-term is 42+ weeks (may require induction)
Your OB may adjust your due date after a first-trimester ultrasound — this is the most accurate method (within ±5–7 days at 8–13 weeks)
After 20 weeks, ultrasound dating becomes less reliable; LMP or first-trimester ultrasound takes precedence

Trimester Breakdown

Trimester	Weeks	Key Milestones
First	Weeks 1–12	Organ formation, first heartbeat, NIPT screening window
Second	Weeks 13–26	Anatomy scan (18–20 wks), fetal movement, glucose test (24–28 wks)
Third	Weeks 27–40	GBS test (35–37 wks), birth prep, weekly visits from 36 wks

Read Trimester Guide → Find an OB-GYN →