Ultrasound due date calculator
An ultrasound report states the pregnancy age on the day of the scan; this turns it into a fixed due date you can refer back to.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter scan date, age on scan: weeks and age on scan: days.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Pregnancy age in days = weeks × 7 + days. Due date = scan date + (280 - pregnancy age in days). Equivalent last period = scan date - pregnancy age in days.
Example
Inputs: Scan date = 2026-03-01, Age on scan: weeks = 12 weeks, Age on scan: days = 3 days. Result: Estimated due date: Thursday, September 10, 2026 (2026-09-10); Equivalent last period date: Thursday, December 4, 2025 (2025-12-04); Pregnancy age on scan day: 12 weeks 3 days.
Limits and caveats
- Ultrasound dating is most accurate before 14 weeks and gets less precise later.
- With several scans, doctors usually keep the earliest reliable one, not the latest.
Questions about this tool
Does the due date change with every scan?
Usually not. The doctor fixes the date from the first accurate scan; later scans track growth rather than reset the date.
How do I read 12w3d on the report?
It means 12 weeks and 3 days of pregnancy on the day of the scan.
Why does the scan date differ from my period date?
Ovulation may have come earlier or later than day 14, and an early scan reflects the baby’s real age more closely.