Estimates the number of days from the first day of the last menstrual period to the due date. This guide explains the formula, use and limitations.
Overview
Estimates the number of days from the first day of the last menstrual period to the due date.
Clinical Significance
Apply the calculated duration to the first day of the LMP. Ultrasound dating and assisted-conception dates can supersede LMP dating.
When to Use
- Use when the calculation is relevant to the clinical question.
- Confirm that the population and units match the validated method.
- Use current and reliable measurements.
How It Is Calculated
- EDD interval = 280 days from LMP, adjusted by cycle length minus 28 days.
Interpretation
- Apply the calculated duration to the first day of the LMP. Ultrasound dating and assisted-conception dates can supersede LMP dating.
- Interpret alongside the full clinical picture and current guidance.
Worked Example
Enter the required measurements in the stated units. MedicalC then applies: EDD interval = 280 days from LMP, adjusted by cycle length minus 28 days.
Patient Considerations
- Consider age, body size, pregnancy, organ function and treatment effects where relevant.
- Repeat the calculation when inputs or clinical status materially change.
Limitations
- Accuracy depends on the quality and units of the entered data.
- The equation may not be validated in every patient population.
- This tool does not replace clinical judgement or specialist advice.
Clinical Pearls
- Check units before calculating.
- Document the source and timing of each input.
- Use trends where clinically appropriate.
Common Mistakes
- Mixing SI and conventional units.
- Using non-contemporaneous measurements.
- Treating the output as a diagnosis or prescription.
Evidence Base
The implemented calculation follows the published or guideline-based relationship: EDD interval = 280 days from LMP, adjusted by cycle length minus 28 days.
Frequently Asked Questions
What does the Estimated Due Date by Nägele Rule calculator do?
Estimates the number of days from the first day of the last menstrual period to the due date.
Can the result be used alone?
No. Use it as decision support with clinical assessment and current guidance.
Why might the result be misleading?
Incorrect units, poor measurement quality or use outside the validated population can produce misleading results.
Should it be recalculated?
Recalculate when relevant measurements or the clinical condition change.
References
- ACOG Committee Opinion: Methods for Estimating the Due Date. — Primary publication, guideline or established source supporting the calculation.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026