Pregnancy Due Date Calculator

Naegele's rule is the standard clinical convention for calculating an estimated date of delivery (EDD) based on a 280-day (40-week) human gestational duration measured from the first day of the last menstrual period (LMP).

• •Classic Formula: EDD = LMP + 1 year - 3 months + 7 days (adjusted for non-28 day cycles).
• •Conception Window: Typically occurs 14 days after LMP in standard cycles.
• •Trimester Milestones: 1st Trimester (Weeks 1–13), 2nd Trimester (Weeks 14–27), 3rd Trimester (Weeks 28–40+).

While clinical formulas provide valuable reference ranges, biological individuality plays a critical role in human physiology.

• •Only approximately 4% of births occur precisely on the calculated estimated due date.
• •Irregular menstrual cycles, polycystic ovarian syndrome (PCOS), or recent contraceptive use introduce estimation errors.
• •First-trimester crown-rump length (CRL) ultrasound scan performed by an obstetrician remains the definitive gold standard for clinical pregnancy dating.