Ultrasound Due Date Calculator
Enter your ultrasound scan date and gestational age in weeks/days, or use CRL in millimeters for early scans.
Ultrasound Due Date Calculator
How to Calculate Due Date from Ultrasound
An ultrasound due date calculation uses two pieces of information: the date of the scan and the baby’s gestational age as measured by the sonographer. Our ultrasound due date calculator takes these inputs and works backward to find your estimated due date using the formula: EDD = Scan Date + (280 days − Gestational Age in days).
Using CRL (Crown-Rump Length)
In early pregnancy (6–13 weeks), the most accurate measurement is the CRL — a straight-line measurement from the top of the embryo’s head to the bottom of its torso. Our CRL calculator converts this millimeter measurement to gestational age using validated tables. A CRL of 10mm corresponds to approximately 7 weeks 1 day, while a CRL of 60mm is approximately 12 weeks 3 days.
CRL Reference Chart
| CRL (mm) | Gestational Age | Weeks + Days |
|---|---|---|
| 10 mm | 50 days | 7w 1d |
| 20 mm | 56 days | 8w 0d |
| 30 mm | 69 days | 9w 6d |
| 45 mm | 80 days | 11w 3d |
| 60 mm | 87 days | 12w 3d |
| 70 mm | 91 days | 13w 0d |
| 84 mm | 97 days | 13w 6d |
First vs Second Trimester Scans
First-trimester scans (8–13 weeks) have a margin of error of about ±5–7 days. Second-trimester scans (14–22 weeks) have a margin of ±10–14 days. After 28 weeks, fetal growth varies considerably between babies, making gestational age estimation from measurements much less reliable. This is why ACOG recommends confirming your EDD in the first trimester if possible.
Frequently Asked Questions
Common questions answered by our medical team