aug or early sept... to find out a more accurate date, take your due date and a calendar and count back 38 weeks.
due dates are estimates based on the average cycle length of 28 days and the average pregnancy length of 40 weeks. since ovulation occurs 2 weeks after the first day of your last period, the date of conception is actually considered being 2 wks pregnant. ----yep, it's confusing!--- =)
here's an example assuming this woman has a 28 day cycle:
she has a period start august 13. 2 weeks later she'd ovulate on the 27th. 38 weeks later, her due date would be may 6th.
since sperm live in you for up to 3 days, it's possible that this woman could have had sex resulting in pregnancy on aug. 25, 26, or 27.
here's a site w/more in depth info: http://www.wdxcyber.com/ninfer11.htm
at 12:42 PM on Nov. 18, 2008