How dates are calculated
By convention, pregnancy is dated from the first day of the last menstrual period (LMP). The estimated due date (EDD) is 280 days (40 weeks) from LMP, or 266 days from conception. Ultrasound dating estimates EDD based on measured gestational age on the day of scan. IVF due dates depend on embryo day at transfer.
Important: This tool is for education only and not a medical diagnosis. Always consult your clinician for personalized care.