(*Source: A Conception Story: TLC tlc.howstuffworks.com )
When does conception occur?
To conceive, an egg needs to be released from your ovaries (ovulation). Ovulation usually happens about 14 days after the first day of your last period. An egg lives for about 12-24 hours after it’s released. For you to get pregnant, a sperm must fertilize the egg within this time. Sperm can live for up to seven days inside your body. This means, if you have sex up to seven days before you ovulate, or within a day or so of ovulating, you could conceive.
Reference: Department of Health: Pregnancy Book (PDF 11.6Mb)