Estimated Due Date (EDD)

days
Health

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

Formula

EDD = LMP + 280 days + (cycle − 28) days (Naegele's Rule, adjusted for cycle length)
  • Standard Naegele's Rule: EDD = LMP + 280 days (assumes 28-day cycle).
  • Adjustment: add extra days for cycles longer than 28 days.
  • Gestational age = weeks from first day of LMP.
  • Ultrasound dating is more accurate after 10 weeks.

LMP January 1, 2025, 28-day cycle

Inputs
  • First Day of Last Menstrual Period: 2025-01-01
  • Cycle Length: 28 days

EDD = Jan 1 + 280 days = October 8, 2025.

Frequently asked questions

How accurate is the due date?
Only about 5% of babies are born on their EDD. A normal term pregnancy is 37–42 weeks. Ultrasound at 11–14 weeks gives the most accurate estimate.