Due Date Calculator: How It Works
How is a due date calculated? Enter your last period, conception date or a known due date to estimate the due date, current pregnancy week and progress.
A due date is typically estimated as 280 days (40 weeks) after the first day of your last menstrual period. This is the standard Naegele’s rule used by clinics worldwide.
If you know your conception date instead, the due date is about 266 days (38 weeks) later, since ovulation usually happens around two weeks after the period starts.
The calculator also shows your current pregnancy week, trimester and overall progress, all based on today’s date versus the estimated last period.
Note: this is an estimate. Only about 5% of babies arrive exactly on the due date, so treat it as a window — always follow your doctor’s assessment.