Estimates the expected date of delivery from the first day of the last menstrual period. This clinical guide explains the inputs, method, interpretation, limitations and evidence supporting the tool.
Overview
Estimated Due Date is a Obstetrics & Gynaecology tool that uses January to produce a structured clinical result. Use it for the clinical purpose described by the calculator and only in an appropriate patient population.
Clinical Significance
The result supports consistent assessment, calculation and communication. It should be combined with the full history, examination, investigations, trajectory of illness and local clinical guidance.
When to Use
- Use when the clinical question matches the stated purpose of Estimated Due Date.
- Confirm that the patient falls within the population for which the method is intended.
- Use current and accurately measured inputs, with the correct units and definitions.
How It Is Calculated
- $estimated_due_date = $lmp->modify(
Interpretation
- Interpret the reported value or category using the explanation displayed with the result.
- Escalate assessment when the clinical picture is more concerning than the calculated category.
Worked Example
Enter a clinically consistent example set of January. The calculator then applies the established Estimated Due Date logic and displays the resulting value or category with its interpretation.
Patient Considerations
- Consider age, comorbidity, pregnancy, organ dysfunction, treatment already given and whether the patient differs from the original validation population.
- Review trends and clinical deterioration rather than relying only on a single calculation.
Limitations
- The tool may perform differently outside its derivation and validation settings.
- Missing, estimated, delayed or incorrectly converted inputs can materially alter the result.
- The calculation cannot account for every diagnosis, contraindication or urgent clinical feature.
Clinical Pearls
- Check each input against the calculator definition before submission.
- Document the component values as well as the final score or calculated result.
- Repeat the calculation when relevant observations, laboratory results or treatment change.
Common Mistakes
- Using the tool for an ineligible patient or a different clinical purpose.
- Entering values in the wrong units or selecting a category from incomplete information.
- Allowing a reassuring result to override significant symptoms, examination findings or clinical deterioration.
Evidence Base
Estimated Due Date is based on the established equation, criteria or scoring system implemented in the calculator. Clinical performance depends on the original evidence base, subsequent validation studies and correct application to the intended population.
Frequently Asked Questions
What is Estimated Due Date used for?
Estimates the expected date of delivery from the first day of the last menstrual period.
Which inputs are required?
The calculator uses January. Check the displayed units and category definitions before entry.
Can the result be used on its own?
No. It supports but does not replace clinical assessment, investigation, local pathways or specialist advice.
When should the calculation be repeated?
Repeat it when a relevant clinical observation, laboratory value, treatment or the patient’s condition changes.
References
- Original publication or authoritative clinical guidance for Estimated Due Date. — Primary publication or authoritative guidance supporting this calculator.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026
