The percentage of the population that "will have PTSD at some point in their lives," according to the VA's National Center for PTSD.
Going through trauma is not rare. About 6 of every 10 men (or 60%) and 5 of every 10 women (or 50%) experience at least one trauma in their lives. Women are more likely to experience sexual assault and child sexual abuse. Men are more likely to experience accidents, physical assault, combat, disaster, or to witness death or injury.
About 8 million adults have PTSD during a given year. This is only a small portion of those who have gone through a trauma.