About 11 to 20 out of every 100 veterans (or between 11 and 20%) who served in operations Iraqi Freedom and Enduring Freedom have PTSD in a given year.
About 12 out of every 100 Gulf War Veterans (or 12%) have PTSD in a given year.
About 15 out of every 100 Vietnam veterans (15%) were currently diagnosed with PTSD when the most recent study of them (the National Vietnam Veteran Readjustment Study) was conducted in the late 1980s. It’s believed that 30% of Vietnam veterans have had PTSD in their lifetime.
There isn't a exact percentage for all the veterans in the US but i hope this helps!