Ultrasound Due Date Calculator – EDD from Scan Date & GA

Updated Aug 2025 · Written by

Enter your ultrasound date and the gestational age reported on the scan (weeks + days) to get your estimated due date.

EDD: —
Gestational age today: —
Methodology & sources

EDD from ultrasound: EDD = scan date + (280 days − measured gestational age at scan). This mirrors standard obstetric dating where 40 weeks is 280 days from LMP; early ultrasound dating commonly supersedes LMP when they differ.

See How it works and Data sources for details and citations.

Frequently asked questions

How is due date calculated from ultrasound?
EDD = scan date + (280 days − the gestational age reported on the scan). Early ultrasound often provides the most reliable dating.
What if this EDD is different from my LMP-based EDD?
Clinicians often replace LMP dating with early ultrasound dating if they disagree meaningfully. Follow your care team’s assigned EDD.
Does it matter which trimester the scan was done?
First-trimester scans are generally most accurate for dating. Later scans may be used to confirm or adjust.
Can I use CRL (crown–rump length) instead of weeks/days?
This tool uses scan-reported weeks/days. A CRL→GA helper may be added later.