Pregnancy Due Date Calculator

Only about 5% of babies are born on their exact due date. The calculation is most accurate for women with regular 28-day cycles. Ultrasound dating in the first trimester can refine the estimate.

Naegele's Rule estimates due date by adding one year, subtracting three months, and adding seven days to the first day of the last menstrual period — equivalent to 280 days or 40 weeks.