Think of your monthly cycle in two parts: B.O. (before ovulation) and A.O. (after ovulation). You’re most fertile two to three days B.O. and 12 to 24 hours A.O. But, since you can’t pinpoint exactly when ovulation occurs, it's best to build in a little cushion. Sperm can live in your reproductive tract for three days, but your egg only lives 12 to 24 hours A.O. Ideally, then, sperm will be in place to greet the egg as it arrives. That means figuring out when you’re likely to ovulate, and starting the sex rompfive or six days prior. Don’t go overboard, though. Limit yourselves to sex every other day, because too much sex can deplete your husband's sperm count.