How is the Due Date Calculated?
This calculator uses Naegele's rule, which is the standard method used by obstetricians. The rule calculates the Estimated Date of Delivery (EDD) by adding one year, subtracting three months, and adding seven days to the first day of your last menstrual period (LMP).
Accuracy of Due Dates
Only about 4% to 5% of babies are born on their exact estimated due date. It is completely normal to deliver anywhere between 37 and 42 weeks of pregnancy.