What Is Gestational Age? The 2-Week Difference Explained
One of the most confusing aspects of early pregnancy dating is discovering that you are already considered “4 weeks pregnant” on the day of your missed period, even though fertilization occurred only about 2 weeks prior.
Gestational Age vs. Conceptional Age
- Gestational Age (Menstrual Age): Measured from the first day of your last menstrual period (LMP). It is standard in clinical obstetrics because menstrual onset is a visible, recorded event. Standard duration: 40 weeks (280 days).
- Conceptional Age (Embryonic Age): Measured from the actual biological moment of fertilization (conception). Standard duration: 38 weeks (266 days).
Key Takeaway:
Gestational Age is always approximately 2 weeks older than the biological embryonic age of the developing fetus.
Check Your Current Gestational Age
Track your exact weeks and days with our Pregnancy Calculator.
Calculate Gestational AgeClinical Accuracy & Medical Disclaimer
This calculator provides educational gestational estimates based on standard obstetric formulas (such as Naegele's Rule and 280-day gestational conventions). Only ~4–5% of babies deliver precisely on their calculated due date; 80% deliver within 37 to 42 completed gestational weeks. This tool does not diagnose medical conditions or substitute for prenatal ultrasounds and professional obstetric guidance.