Pregnancy Calculator

Pregnancy due dates are calculated using Naegele's Rule — the standard convention used by ACOG, Mayo Clinic, and most obstetricians: take the first day of your last menstrual period (LMP), add 280 days (40 weeks), and that's your estimated due date (EDD). This calculator also shows current gestational age, trimester, and key upcoming milestones based on the same LMP-based timeline. It's important to understand what these dates actually mean: gestational age is counted from the LMP, not from conception, so 'you are 8 weeks pregnant' typically means conception happened about 6 weeks ago. The EDD is an estimate — fewer than 5% of babies are actually born on their due date, and about 80% arrive within the two-week window around it. If you know your conception date (from IVF or precise ovulation tracking), the math shifts: add 266 days to conception instead. Early ultrasound (before 14 weeks) is more accurate than LMP-based dating, especially if your cycles are irregular, and your provider may adjust your due date based on it. This tool gives you the standard textbook calculation; always defer to your obstetrician's dating for medical decisions.