Learn about the best time to have intercourse for pregnancy and fertility advice. Ovulation usually occurs on day 14 of a 28-day menstrual cycle or day 16 of a 30-day cycle. The egg only lives for 12-24 hours, while sperm can live for up to 2-5 days. Therefore, it's best to have sex on the day of ovulation or the day before. Having sex more than 24 hours after ovulation is unlikely to increase the chances of pregnancy.