Pregnancy Due Date Calculator

The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation on day 14. Alternatively, your healthcare provider may calculate it based on conception date (add 266 days) or via ultrasound measurements, which are particularly accurate in the first trimester when the embryo is growing at a predictable rate.

Only about 5% of babies are born on their estimated due date. Most births occur within a window of 2 weeks before or after the due date. First-trimester ultrasound (performed at 8-13 weeks) is the most accurate dating method, with a margin of error of ±5-7 days. Due dates calculated from LMP can be off if your cycle is irregular or longer or shorter than 28 days.

A pregnancy is considered full term when it reaches 39 weeks 0 days through 40 weeks 6 days. Early term is 37-38 weeks and 6 days. Late term is 41-41 weeks and 6 days, and post-term is 42 weeks or beyond. Babies born before 37 weeks are premature (preterm). The American College of Obstetricians and Gynecologists (ACOG) recommends that non-medically indicated deliveries be scheduled no earlier than 39 weeks.