Conception happen several hours after ovulation. Ovulation happens 14 days before the next menstrual cycle starts ... which means that in a 28 day-long cycle, ovulation occurs in the middle of the cycle. Two days before and 2 days after ovulation are considered the "fertile days" of the cycle-when conception is very likely. The 11th day of the menstrual cycle can be considered a fertile day if the cycle lasts 22-26 days.