🍼 Due Date Calculator

Only about 5% of babies are born on their exact due date. Full term is considered 37–42 weeks. The EDD is a midpoint estimate — most births occur within 2 weeks before or after. Early ultrasound (8–12 weeks) is the most accurate way to confirm dating.

Naegele's Rule estimates the due date as LMP + 280 days (40 weeks). It assumes a 28-day menstrual cycle with ovulation on day 14. Women with irregular cycles may need adjustment. This is the method used in this calculator.

First trimester: weeks 1–13 (organ development). Second trimester: weeks 14–26 (rapid growth, movement). Third trimester: weeks 27–40 (weight gain, lung maturation). Each trimester brings distinct developmental milestones.

For IVF, the embryo's age at transfer is known. A day 5 blastocyst transfer subtracts 5 days from the conception equivalent, giving EDD = transfer date + 261 days. Day 3 embryo: EDD = transfer + 263 days.

An early ultrasound (ideally at 8–12 weeks, called a dating scan) provides the most accurate EDD. If the ultrasound date differs from LMP date by more than 7–14 days, the ultrasound date is typically used.