The Best Time To Get Pregnant: You're most likely to get pregnant if you have sex within a day or so of ovulation (releasing an egg from the ovary). This is usually about 14 days after the first day of your last period, if your cycle is around 28 days long. An egg lives for about 12-24 hours after being released. For pregnancy to happen, the egg must be fertilised by a sperm within this time. Sperm can live for up to 7 days inside a woman's body. So if you've had sex in the days before ovulation, the sperm will have had time to travel up the fallopian tubes to "wait" for the egg to be released. It's difficult to know exactly when ovulation happens, unless you are practising natural family planning, or fertility awareness.