Due Date Calculator (by Ultrasound Biometry)
Medical-grade tool to recalculate EDD using Crown-Rump Length (CRL) or gestational age from a scan. Validates LMP dates.
About
Ultrasound biometry in the first trimester is the gold standard for pregnancy dating. Between 6 and 14 weeks of gestation, the growth of the embryo is extremely uniform across the population, making the Crown-Rump Length (CRL) a more accurate predictor of the Estimated Date of Delivery (EDD) than menstrual history.
This tool serves as a "Medical Check" to verify dates. Clinical guidelines typically suggest re-dating the pregnancy if the ultrasound date differs from the LMP date by more than 5 to 7 days. It uses standard regression logic to derive Gestational Age (GA) from the physical measurement of the fetus in millimeters.
Formulas
When Gestational Age (GA) is known from the scan, the formula is:
If calculating from CRL (Crown-Rump Length), the tool uses a simplified Robinson curve approximation for weeks 6-14:
Reference Data
| CRL (mm) | Gestational Age (Approx) | Growth Rate |
|---|---|---|
| 5 mm | 6 Weeks 1 Day | Fetal Pole Visible |
| 10 mm | 7 Weeks 0 Days | Heartbeat distinct |
| 20 mm | 8 Weeks 4 Days | ~1mm / day |
| 50 mm | 11 Weeks 5 Days | Limbs developed |
| 80 mm | 13 Weeks 6 Days | End of Trimester 1 |