Pregnancy Due Date Calculator

The due date is an estimate, not a precise prediction. Only about 5% of babies are born on their due date, and most arrive within two weeks before or after. First-trimester ultrasound dating is the most accurate method and may adjust the LMP-based estimate.

Naegele's rule is the standard method for estimating due date: add 280 days (40 weeks) to the first day of the last menstrual period, or equivalently, add 7 days and subtract 3 months. It was developed by German obstetrician Franz Naegele in the 1830s and remains widely used today.

Yes. If an early ultrasound (first trimester) shows a significantly different estimated gestational age than the LMP-based calculation, your doctor may adjust your due date. Later ultrasounds are less accurate for dating and less likely to change the due date.

A full-term pregnancy is between 39 weeks and 40 weeks 6 days. Early term is 37-38 weeks, late term is 41 weeks, and post-term is 42+ weeks. The American College of Obstetricians and Gynecologists (ACOG) recommends against elective delivery before 39 weeks unless medically indicated.

For IVF pregnancies, the calculation is more precise. With a 5-day embryo transfer, the due date is approximately 261 days after the transfer date (or 280 days minus 19 days). With a 3-day transfer, it is approximately 263 days after transfer. Your fertility clinic will provide the most accurate estimate.