Naegele Due Date Calculator
Estimated delivery date from last menstrual period with trimester boundaries.
Understanding this tool
Why nurses use it
Naegele’s rule estimates expected delivery date (EDD) from the last menstrual period (LMP). Nurses and midwives use it for antenatal dating, gestational age documentation, and care planning when early ultrasound is not yet available.
When to use it
Use when LMP is known and cycles are reasonably regular. Ultrasound dating overrides if dates differ significantly.
Calculate
How to use this calculator
- Enter the first day of the LMP.
- Read estimated delivery date and approximate gestational age.
- Confirm with ultrasound biometry when available.
How the calculation works
EDD = LMP + 280 days (or +7 days, −3 months, +1 year as needed). Assumes a 28-day cycle with ovulation on day 14.
Formula used by this tool — verify units before applying at the bedside.
Worked example
Limitations & clinical notes
- Assumes regular 28-day cycles.
- Ultrasound biometry is preferred when LMP is uncertain.
References
Key sources: ACOG — gestational dating.
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Disclaimer: This calculator is for educational and bedside double-check purposes only. It does not replace institutional protocols, prescriber orders, pharmacist verification, or clinical judgment. Always follow your local policies — especially for high-risk medications, infusions, pediatrics, and critical care. If the patient is acutely unwell, escalate immediately rather than relying on any calculator output.