If i'm 31 weeks pregnant, what date did i most likely concieve?

29 weeks ago: All pregnancy dates for naturally-occurring pregnancies are estimates. The estimated conception date is 2 weeks after the official start date of the pregnancy. Thus, if 31 weeks pregnant now, one can just get a calendar and count back 29 weeks to arrive at the estimated conception date. The estimate arrived at is an approximate date, plus or minus one week.