Due date calculator
Find out how many weeks pregnant you are, your estimated due date, and when your scans and tests fall on the calendar.
How the due date is calculated
Clinicians add 280 days (40 weeks) to the first day of your last menstrual period (Naegele’s rule), adjusting if your cycle is longer or shorter than 28 days. From a conception date, the due date is 266 days later. For IVF, it’s 263 days after a day-3 transfer or 261 days after a day-5 transfer.
If an early ultrasound gives a different date, your care team will usually use the scan date, because scan dating in the first trimester is more accurate.