How accurate is this estimate?

Only about 5% of babies are born exactly on their due date; this is a statistical estimate, and an ultrasound provides a more precise dating.

Pregnancy Due Date Calculator

Using Naegele's rule, this calculator estimates a due date as 280 days (40 weeks) after the first day of the last menstrual period.

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Formula

Due Date = LMP + 280 days

How Pregnancy Due Dates Are Calculated (Naegele's Rule)

The 280-day rule behind due date estimates, and why only a small fraction of babies arrive exactly on that date.

Tracking a Pregnancy Timeline: Due Dates, Weeks, and What the Numbers Mean

How due date calculations and weeks-pregnant tracking work together, and why early estimates often get refined later.

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