Due Date by Ultrasound Calculator – CRL-Based Dating
Estimate your due date from the Crown-Rump Length (CRL) measured at an early ultrasound (6–14 weeks). Uses the Robinson formula. Enter CRL in mm and the ultrasound date.
Due Date by Ultrasound Calculator
Estimate due date from Crown-Rump Length (CRL) measured at 6–14 weeks. Uses the Robinson formula.
Robinson formula
GA (days) = 8.052 × √(CRL) + 23.73
CRL in mm. Due date = Ultrasound date + (280 − GA days).
Why use ultrasound for due date?
When the last menstrual period (LMP) is uncertain or cycles are irregular, ultrasound dating can be more accurate than Naegele's rule. The Crown-Rump Length (CRL) measured in the first trimester correlates well with gestational age. The Robinson formula, published in 1975, is widely used and validated for CRL between about 1 and 84 mm (roughly 6–14 weeks). Your healthcare provider may use this or a similar formula to assign or adjust your due date.
This calculator is for educational purposes. Always rely on your provider's official due date for clinical decisions. If your ultrasound report includes a different formula or dating method, your provider's result may differ slightly from this estimate.