Due Date Calculator (EDD)

ℹ️ About This Calculator

The Due Date Calculator (EDD) is a standard obstetric calculation tool used to derive pregnancy dating parameters, assess fetal growth, evaluate labour readiness, or estimate obstetric outcomes using validated formulas and reference data. Accurate obstetric calculations are fundamental to safe antenatal care — errors in gestational age, estimated fetal weight, or induction readiness assessment directly affect clinical decisions about screening test timing, corticosteroid administration, delivery planning, and neonatal management.

Gestational age is the most fundamental parameter in obstetric care — it determines the schedule of every antenatal assessment, screening test, and intervention from first trimester viability to delivery planning. The Due Date Calculator (EDD) applies the appropriate validated formula or reference standard — whether Naegele's Rule for due date calculation, Hadlock equations for fetal weight estimation, or Bishop scoring for cervical assessment — to provide a clinically reliable result.

The exact formula and variable definitions used by this calculator are shown in the Formula section below. For obstetric calculations, formula transparency matters because different equations and charts have different populations of origin, and clinicians should know which reference they are applying. For example, Hadlock equations for estimated fetal weight were derived from predominantly white American fetuses — they may produce different accuracy in other ethnic populations.

Important limitations: LMP-based dating (Naegele's Rule) assumes a regular 28-day cycle with ovulation on day 14. For patients with irregular cycles, unknown LMP, or cycles substantially longer or shorter than 28 days, first-trimester ultrasound dating by CRL measurement is significantly more accurate and should be used per ACOG guidelines. Fetal weight estimations have an inherent error of approximately ±15–20% regardless of the formula used. The Due Date Calculator (EDD) provides estimates — clinical findings, ultrasound measurements, and professional judgment define the management plan.

All calculations run in your browser only. No obstetric data, LMP dates, fetal measurements, or clinical information is transmitted to any server or stored anywhere. This ensures full compliance with healthcare data privacy requirements when using the tool during clinical consultations.

These calculators support evidence-based obstetric care — they do not replace it. All pregnant women should receive regular antenatal care from a qualified obstetrician or midwife. Contact your maternity care provider promptly for: vaginal bleeding at any gestation, decreased fetal movement after 24 weeks, symptoms of pre-eclampsia (severe headache, visual disturbance, epigastric pain, oedema), signs of preterm labour, or any other concerns about pregnancy. If in doubt, always seek prompt obstetric assessment.

📌Clinical Reference: Naegele's rule — ACOG

📋 How to Use This Calculator

1. 1

   Confirm the last menstrual period date

   Enter the first day of the last normal menstrual period (LMP). Ensure the date is reliable — a patient with irregular cycles or uncertainty about the LMP date will require ultrasound dating.

2. 2

   Enter clinical measurements as required

   For fetal weight estimation, input ultrasound biometric measurements (BPD, HC, AC, FL). For Bishop Score, enter the cervical examination findings at the time of assessment.

3. 3

   Calculate the obstetric parameter

   The tool applies the validated formula and returns the gestational age, EDD, fetal weight estimate, or clinical score. The result is displayed with the applicable reference range.

4. 4

   Compare with ultrasound findings

   For pregnancy dating, compare the LMP-derived EDD with first-trimester ultrasound dating. If the discordance is >5–7 days in the first trimester, the ultrasound date takes precedence per ACOG guidelines.

5. 5

   Document and plan antenatal care

   Record the calculated GA and EDD in the patient's obstetric record. Gestational age determines the schedule for antenatal screening tests, growth scans, and delivery planning.

🎯 When to Use This Calculator

💡 Clinical Pro Tips