Our conception calculator, also known as a reverse due date calculator, estimates when your pregnancy was conceived.

When calculating conception based on the due date, we subtract 266 days (38 weeks). When using the last menstrual period, we add 14 days.

The resulting date is your estimated day of ovulation. Since conception occurs soon after ovulation, this is the most likely date of conception. Your estimated conception window is 3 days before and 3 days after your estimated date of ovulation (EDO).

If you are not currently pregnant, use our Ovulation Calendar instead.