DYU FERTILITY · PATIENT TOOLS
Pregnancy calculator
Estimate your due date, pregnancy weeks and trimester dates using your last period, a confirmed due date, ultrasound dating or a known conception date.
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
Pregnancy dating counts 40 weeks to the estimated due date. For regular cycles, we add 280 days to the first day of your last period and adjust for cycle length. A known conception date adds 266 days. Scan dating uses the weeks and days recorded on your report.
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 ↗