the due date is a guess based on guessed conception, so the date of conception can only be guessed from due date.
the estimated due date is actually 38 weeks after the guessed conception date, which is guessed to be 2 weeks after the last menstrual period. can you tell it's all guesses? ;)
if your last menstrual period started on november 11, a doctor might estimate that you conceived on november 25, and then estimate your due date to be august 18th.
at 7:53 PM on Jan. 6, 2010