DYU FERTILITY · PATIENT TOOLS
Conception date calculator
Estimate when conception may have happened using your due date, last period or the pregnancy dating on your ultrasound report.
YOUR ESTIMATE
Your result will appear here
Enter the details you know, then select Calculate. If your dates are uncertain, your clinician can help interpret your scan report.
How the estimate works
We count back 266 days from the estimated due date. When you enter a period date, the estimate assumes ovulation about 14 days before the next period. Ultrasound dating works backwards from the gestational age recorded on your scan.
How accurate are these dates?
Cycle timing varies, and a calendar cannot confirm exactly when fertilisation happened. Irregular cycles make period-based estimates less useful. A dating scan can help your clinician establish a due date. Keep using the date agreed with your maternity team rather than changing it after each scan.
For pregnancy after an embryo transfer, use our IVF due-date calculator with the embryo age recorded by your clinic.
ACOG: Methods for estimating the due date ↗NHS: Pregnancy due date calculator ↗