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Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP.
Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP.
Enter values above and click Calculate — results will appear here with the formula explained.
Naegele's rule estimates due date as 280 days from the first day of last menstrual period, assuming a 28-day cycle and ovulation on day 14. It yields 40 weeks gestation.
This is an estimate for informational purposes only, not medical advice. Ultrasound dating is more accurate — confirm with a clinician, especially with irregular cycles.
Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP. Formula: Due date = LMP + 280 days (40 weeks) = LMP + 1 year - 3 months + 7 days.
Naegele's rule estimates due date as 280 days from the first day of last menstrual period, assuming a 28-day cycle and ovulation on day 14. It yields 40 weeks gestation.
This is an estimate for informational purposes only, not medical advice. Ultrasound dating is more accurate — confirm with a clinician, especially with irregular cycles.
If LMP is 2026-01-01, adding 280 days gives due date 2026-10-08, about 40 weeks later.
Formulas are standard public references (see our methodology). External standards are cited in the text where they apply.
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