When did you conceive if your last normal period was August 5?

I went to http://www.intmed.mcw.edu/clincalc/pregnancy.html and put in Aug 5th as your last period and it shows conception occured on August 19th. Remember, sperm can live in a womans body for 5-7 days. So the sperm could have been from sex up to a week before that day. This is also based on a 28 day cycle, so add or subtract days depending on how long your cycle is.