September 2026
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Pregnancy due date calculator
Estimate your due date using Naegele's rule (LMP + 280 days).
Estimate, not a diagnosis. This tool gives an educational estimate based on the numbers you enter. It cannot account for your individual health history — consult a healthcare professional for anything clinical.
How this is calculated
We apply Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period, with a small adjustment if your average cycle differs from 28 days.
Outputs
- Estimated due date
- Current gestational age
Limitations
Ultrasound dating can be more accurate, especially if your LMP is uncertain. Use this estimate as a guide and confirm clinically.
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Frequently asked questions
How is a due date calculated from my last period?
Using Naegele’s rule: 280 days (40 weeks) are added to the first day of your last menstrual period. A small adjustment is made if your average cycle length differs from the standard 28 days.
How accurate is a due date calculated this way?
Only about 5% of babies are born on their exact due date, and most arrive within about two weeks of it either way. Naegele’s rule is a standard estimate, and ultrasound dating in early pregnancy is generally more precise if your last period date is uncertain.
What if I have irregular cycles?
Naegele’s rule assumes a fairly regular 28-day cycle, so it becomes less reliable with irregular cycles. An early ultrasound is usually recommended for more accurate dating in that case.