Pregnancy Due Date & Trimester Milestone Calculator
Calculate your estimated due date (EDD), gestational age, fetal development milestones, and trimester transitions using Naegele’s Rule, conception date, or IVF transfer dates.
# Calculation Pipeline (Chain of Thought)
- Step 1 (Naegele's Standard Calculation):
Estimated Due Date (EDD) = LMP Date + 280 Days + (Cycle Length - 28 Days). - Step 2 (Conception-Based Calculation):
EDD = Conception Date + 266 Days (38 post-ovulatory weeks). - Step 3 (Gestational Age Pipeline):
Current Gestational Age = Current Date - LMP Date (formatted as Weeks + Days). - Step 4 (Trimester Milestone Classification): 1st Tri (Weeks 1-13), 2nd Tri (Weeks 14-27), 3rd Tri (Weeks 28-40), Full Term (Weeks 39-40+6d).
Decision Rule: Obstetric Classification: Full Term is defined between 39 weeks 0 days and 40 weeks 6 days. Deliveries between 37w0d and 38w6d are Early Term.
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| PREGNANCY DUE DATE & TRIMESTER TIMELINE |
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[ First Day of LMP ] OR [ Conception Date ] OR [ IVF Transfer Date ]
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[ Naegele's 280-Day Engine / 266-Day Embryonic Counter ]
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[ ESTIMATED DUE DATE (EDD) ] (40 Weeks / 280 Days from LMP)
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[ 1st Trimester ] [ 2nd Trimester ] [ 3rd Trimester ]
Weeks 1 to 13.6 Weeks 14 to 27.6 Weeks 28 to 40+
• Organogenesis • Anatomy Scan (W18-22) • Growth & Lung Maturity
• CRL Ultrasound • Quickening / Kicks • Full Term @ W39-40
Frequently Asked Questions
What is Naegele’s Rule and how accurate is it?
Naegele’s rule calculates the Estimated Due Date (EDD) by adding 1 year, subtracting 3 months, and adding 7 days to the first day of the last menstrual period (280 days total). Approximately 4–5% of babies are born on their exact due date, while 80–90% arrive within two weeks before or after.
How does an early dating ultrasound modify the LMP due date?
If a first-trimester ultrasound crown-rump length (CRL) measurement differs from the LMP due date by more than 5 to 7 days, the ultrasound date becomes the official clinical due date.
How do you calculate a due date for IVF 3-day or 5-day embryo transfers?
For a 5-day blastocyst transfer: Due Date = Transfer Date + 261 days (Transfer Date + 266 days - 5 days). For a 3-day transfer: Due Date = Transfer Date + 263 days.
What are the exact gestational weeks for each trimester?
First Trimester: Conception/LMP through Week 13 (+6 days). Second Trimester: Week 14 through Week 27 (+6 days). Third Trimester: Week 28 through delivery (Week 40+).
Obstetric Milestones & Prenatal Protocols
- First Trimester Folate Supplementation: Take 400–800 mcg of active methylated folate/folic acid daily during preconception and the first 12 weeks to support neural tube closure.
- Anatomy Ultrasound Timing (Weeks 18–22): Schedule the comprehensive Level II anatomy ultrasound between 18 and 22 weeks to evaluate fetal organ development, placental location, and amniotic fluid index.
- Gestational Diabetes Screening (Weeks 24–28): Complete the standardized 50-gram 1-hour Oral Glucose Tolerance Test (OGTT) between 24 and 28 weeks to screen for gestational carbohydrate intolerance.
- Group B Strep (GBS) Screening (Weeks 36–37): Obtain the standard vagino-rectal GBS swab screening at weeks 36–37 to determine if intrapartum prophylactic antibiotics are indicated during labor.