how to calculate conception date
To Help You calculate ... Pregnancy due date (or birthday): Select the month, day, and year your baby is due. Note that you can also select any birthday to calculate when you or someone else was most likely conceived. Estimated conception date: This is 266 days (38 weeks) subtracted from the selected pregnancy due date (the average human gestation period per Naegele's Rule). Last period date: This is 14 days prior to conception (assuming ovulation occurred on day 14 of your menstrual cycle).