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Pregnancy Due Date Calculator
Calculate your estimated due date from the first day of your last period.
About This Calculator
Naegele's rule calculates due date as 280 days (40 weeks) from the last menstrual period — established in 1812. Studies show the average gestation is actually 40 weeks 5 days for first-time mothers. Ultrasound dating in the first trimester is more accurate than LMP dating alone.