Pregnancy Due Date Calculator

First day of last menstrual period

Average cycle length (days)

Estimated Due Date

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Weeks pregnant today

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Current trimester

This is an estimate based on standard calculation methods, not a medical diagnosis. Only about 5% of babies arrive on their exact due date. Please confirm dates and monitor your pregnancy with a qualified healthcare provider.

How due dates are estimated

This calculator uses Naegele's Rule, the standard method used by most healthcare providers: it takes the first day of your last menstrual period, adjusts for your typical cycle length, and adds 280 days (40 weeks) to estimate the due date.

This method assumes a fairly regular cycle. If your cycles are irregular, or if conception is known from other methods (like IVF), an ultrasound-based estimate from your doctor will usually be more accurate.

Understanding trimesters

Pregnancy is typically divided into three trimesters: the first (weeks 1-13), second (weeks 14-27), and third (weeks 28-40). Each trimester is associated with different stages of fetal development and different common experiences for the pregnant person.