If a woman has an average 28 day menstrual cycle, it is possible for her to get pregnant 5 days after her period ends. According to WebMD, sperm can live in a woman's body for up to 6 days. A woman that has sex five days after her period could still have live sperm when she ovulates.
Ovulation occurs around day 14 of a woman's menstrual cycle, assuming that she has a 28 day cycle. If her period lasts for 5 days, 5 days after her period ends would put her at day 10 of her cycle. Considering the life span of sperm, sex on cycle day 10 falls within a woman's fertile time and can result in a pregnancy.
It must be noted that it is normal for a woman's menstrual cycle to be anywhere from 21 to 35 days in length. For a woman with a cycle that is longer or shorter than 28 days, it may not be possible to get pregnant 5 days after her period ends. The time that ovulation occurs varies based on how long a woman's cycle is.