Due Date Calculator

The most common method uses Naegele's rule: Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Only about 5% of babies arrive on their exact due date.

For IVF pregnancies, the due date is calculated from the embryo transfer date. For a Day 3 embryo transfer, add 263 days. For a Day 5 (blastocyst) transfer, add 261 days. This is more accurate than LMP dating.

Early ultrasounds (before 12 weeks) can date pregnancy more accurately by measuring the embryo. If there's a difference of more than 7 days from LMP dating, doctors often use the ultrasound date. Later ultrasounds are less accurate for dating.

Full term is 39-40 weeks. Early term is 37-38 weeks, late term is 41 weeks, and post-term is 42+ weeks. Babies born between 37-42 weeks are generally considered healthy, though outcomes are best at 39-40 weeks.

Due dates are estimates. Only about 5% of babies are born on their due date. About 80% are born within 2 weeks of the due date (38-42 weeks). First-time mothers often deliver closer to 41 weeks.