Pregnancy progress
Trimester bands across the 40 weeks, with a pointer at today.
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Pregnancy
Due Date Calculator
Estimate your baby's due date with Naegele's rule, and see the dates for each pregnancy milestone from your last menstrual period.
Estimated due date
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End of 1st trimester—
End of 2nd trimester—
Viability (24 weeks)—
Full term (37 weeks)—
How it works
Naegele's rule estimates the due date as 280 days (40 weeks) after the first day of your last period, which is the same as subtracting three months and adding seven days (and one year). If you know your conception date instead, the due date is 266 days after it.
From LMP: Due = LMP + 280 days
From conception: Due = conception + 266 days
From conception: Due = conception + 266 days
Due dates are estimates. Most births happen within the two weeks before or after, and an early ultrasound may revise the date.
Frequently asked questions
How accurate is the due date?
Only about 4% of babies are born on their exact due date. It is best treated as the middle of a likely delivery window of roughly 38–42 weeks.
Should I use my period or conception date?
Use your last period if you know it — that is the clinical standard. Use conception only if you are confident of the date, for example with assisted reproduction.