Due Date Calculator

The standard method is Naegele's Rule: take the first day of your last menstrual period (LMP), subtract 3 months, then add 7 days. This gives a 40-week gestational age from LMP, which is the universal clinical standard. If you know your conception date, add 266 days (38 weeks) instead.

A due date is an estimate, not a prediction. Only about 5% of babies are born exactly on their due date. Most full-term babies arrive between weeks 38 and 42. Your OB or midwife may adjust your due date based on an early ultrasound, which is the most accurate dating method available.

Gestational age is measured from the first day of your last period — this is what your doctor uses and what all pregnancy milestones reference. Fetal age (also called embryonic age) is measured from conception, which is typically about 2 weeks after LMP. When your OB says 'you're 12 weeks pregnant,' they mean 12 weeks gestational age.

Most parents start their registry between 16–20 weeks. This gives you time to research big-ticket items (car seat, stroller, crib) before announcing the registry to family, and gets it live in time for a baby shower (which typically happens between weeks 28–34). See our Baby Registry by Trimester guide for a full timeline.

If your cycles are longer or shorter than 28 days, your due date from LMP may be off. The most accurate dating comes from a first-trimester ultrasound (before 13 weeks), which can measure fetal size and estimate gestational age precisely. If there's a significant discrepancy between your LMP date and your ultrasound date, your provider will typically use the ultrasound date.