Menstrual Cycle Counted from the first day of your period to the first day of the following period, the menstrual cycle prepares your body for pregnancy. According to the National Institute of Child and Human Development, most menstrual periods are 28 days in length but can vary from 21 to 35 days and still be normal. Ovulation Usually sometime between day 11 and day 21 of your menstrual cycle, changes in your body's hormones cause a mature egg to be released into your fallopian tube (ovulation), where it is available to be fertilized for up to 24 hours, according to the American Pregnancy Association. Pregnancy According to the American Pregnancy Association, sperm can stay alive in your reproductive tract for up to 5 days. If this sperm penetrates a ripe egg during that time, then pregnancy results. Menstrual Period Unfertilized, a ripe egg travels to your uterus where the thickened uterine lining (endometrium) breaks down, leaving your body in the monthly flow known as your menstrual period. Considerations If you experience a longer menstrual period and a menstrual cycle of average length, then you can easily get pregnant five days after your period; for example, if you have a 7-day period and a 28-day menstrual cycle, then your ovulation window typically begins 4 days following your period, extending to 14 days after your period.