Pregnancy Due Date & Gestational Age Calculator
### Obstetrics & Perinatology: Gestational Age vs. Fetal Age In medical practice, pregnancy duration is measured in **Gestational Age (GA)** starting from the first day of the last menstrual perio...
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📐 Formula
💡 Practical Example
For example, with a Last Menstrual Period of January 1, 2026 and standard 28-day cycle: \. Estimated conception occurred on January 15, 2026. The 2nd trimester begins on April 2, 2026 (Week 14) and the 3rd trimester begins on July 9, 2026 (Week 28).
📖 About Pregnancy Due Date & Gestational Age Calculator
Obstetrics & Perinatology: Gestational Age vs. Fetal Age
In medical practice, pregnancy duration is measured in Gestational Age (GA) starting from the first day of the last menstrual period (LMP), roughly two weeks before actual fertilization occurs.
Pregnancy Classification Definitions (ACOG)
- Early Term: 37 weeks 0 days through 38 weeks 6 days.
- Full Term: 39 weeks 0 days through 40 weeks 6 days (lowest risk of neonatal complications).
- Late Term: 41 weeks 0 days through 41 weeks 6 days.
- Postterm: 42 weeks 0 days and beyond.
How to Use This Calculator
Enter your Calculation Method — select from Last Menstrual Period (LMP, Naegele's Rule), Known Conception / Ovulation Date, IVF 5-Day Blastocyst Transfer Date, Reference Date (YYYY-MM-DD) (e.g. 2026-01-01), and Average Menstrual Cycle Length (Days, for LMP) (e.g. 28). Results update instantly — no submit button needed. Use metric or imperial units as labeled. For the most accurate result, measure height and weight in the morning without shoes.
The Formula
Standard clinical obstetric pregnancy dating formulas:'s Rule (LMP Dating): EDD = LMP Date + 280 days + (Cycle Length - 28) Date Method: EDD = Conception Date + 266 days Day-5 Blastocyst Transfer: EDD = Transfer Date + 261 days Age (weeks): GA = (Today - LMP Date (days)) / (7)
Worked Example
For example, with a Last Menstrual Period of January 1, 2026 and standard 28-day cycle: . Estimated conception occurred on January 15, 2026. The 2nd trimester begins on April 2, 2026 (Week 14) and the 3rd trimester begins on July 9, 2026 (Week 28).
Understanding Your Result
Naegele's Rule (LMP + 280 days) gives the estimated due date — only about 5% of babies arrive on their exact due date. The normal delivery window is 37–42 weeks gestation. Babies born 37–38+6 weeks are "early term" and may have higher risk of respiratory and feeding difficulties than babies born 39–40 weeks. Ovulation typically occurs 12–16 days before the next menstrual period, not necessarily on day 14 — cycle length variation shifts this window significantly.
💡 Expert Health Guidance & Clinical Context
- This calculator uses clinically validated formulas and population reference data published by the WHO and NIH. Results are screening estimates, not medical diagnoses.
- Consult a licensed healthcare provider before making any changes to diet, medication, or exercise based on these results — individual variation is significant.
- Genetics, chronic conditions, and concurrent medications can dramatically affect what a "normal" result means for a specific individual.
- Track your results over time: a single data point is less meaningful than a trend measured consistently across multiple weeks or months.
- The CDC recommends adults receive routine health screenings at least annually. Use these calculations to prepare informed questions for your physician.
- Body composition, lifestyle factors, and stress levels all interact with the metrics shown here. No single number captures your full health picture.
- For pediatric or geriatric populations, reference ranges may differ significantly from the adult standards used in general calculators.
- Always cross-reference results with laboratory tests, clinical examinations, and professional medical evaluation before acting on any finding.
Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.