Due Date Calculator by Last Period

Using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. For a 28-day cycle, this assumes ovulation occurred 14 days after LMP, with conception around that time.

Adjust the cycle length in the calculator. If your cycles are longer than 28 days, your due date will be later. If shorter, it will be earlier. For very irregular cycles, an ultrasound dating is more accurate.

Only about 5% of babies are born on their exact due date. However, about 80% are born within 2 weeks before or after. The LMP method is most accurate for women with regular 28-day cycles.