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About the Pregnancy Calculator
This Pregnancy Calculator estimates your due date, current pregnancy week, and trimester from the first day of your last menstrual period. You also get a week-by-week view of fetal development and key milestones as your pregnancy progresses.
The calculator applies Naegele's rule, the standard obstetric method that adds 280 days, or 40 weeks, to the first day of the last menstrual period. Enter that date, and adjust the cycle length setting if your cycles are longer or shorter than 28 days. Regular cycles give the most reliable estimate. If your cycles are irregular, an early ultrasound can confirm the dating, so consider a healthcare professional for precise dating decisions.
- Enter the first day of your last menstrual period.
- Set your average cycle length if the option appears.
- Review your due date, current week, and milestone timeline.