Calculator input
Formula used
EDD = Scan Date + (280 − Gestational Age in Days)
Gestational Age in Days = (Weeks × 7) + Days
Estimated Conception Date = EDD − 266 days
This calculator converts the ultrasound gestational age into total days, subtracts that value from 280, and adds the remaining days to the scan date.
It also shows current gestational age, trimester labels, optional date comparisons, and time remaining to the estimated due date.
How to use this calculator
- Enter the ultrasound scan date from the report.
- Type the gestational age exactly as weeks and days.
- Select the dating basis that best matches the report.
- Optionally add LMP-based or reported EDD dates for comparison.
- Click Calculate EDD to show the result above the form.
- Download the result as CSV or PDF for records.
Example data table
| Record | Scan Date | GA at Scan | Dating Basis | Calculated EDD |
|---|---|---|---|---|
| Early dating scan | 2026-03-07 | 12w 4d | Crown-rump length dating | 2026-09-15 |
| Routine dating review | 2026-04-10 | 19w 2d | Composite fetal biometry dating | 2026-08-31 |
| Follow-up comparison | 2026-05-01 | 22w 0d | Ultrasound gestational age from report | 2026-09-04 |
Frequently asked questions
1) What does EDD mean?
EDD means estimated due date. It is the expected date of delivery calculated from pregnancy dating information, such as ultrasound gestational age or menstrual dating.
2) Why use ultrasound for EDD?
Ultrasound dating helps estimate pregnancy age when cycle dates are uncertain, unavailable, or different from the scan report. Earlier scans usually support more dependable dating.
3) Can I enter weeks and days separately?
Yes. The calculator asks for gestational age in weeks and days, then converts that information into total days for the EDD calculation.
4) Does this replace the official report?
No. This tool is for education and planning. The formal ultrasound report and your clinician’s dating decision should guide prenatal records and care.
5) Why compare LMP and ultrasound dates?
Comparing dates helps you see whether menstrual dating and ultrasound dating are close together. Large differences should be reviewed with a qualified maternity clinician.
6) Can twins use the same calculator?
You can record a multiple pregnancy label here, but clinical management for twins or higher-order pregnancies still requires individualized professional assessment and follow-up.
7) What does the conception date estimate show?
It shows an approximate conception date by subtracting 266 days from the estimated due date. It is a planning estimate, not proof of conception timing.
8) Can I save the result?
Yes. After calculation, use the CSV or PDF buttons to download a clean summary of the result for personal records or discussion.