You get them per semester, not per year. I believe (But I could be wrong) that a C4C gets 5 for the semester. However; you can earn extra. You can get extras for academics, military, special projects, etc... My son's first year he received some extras because he volunteered to do so altitude studies. They were looking for cadets who grew up and was use to the higher altitude. He also received some extras I believe for his grades.
You get even more each year. By your senior year (C1C) it's a moot point. Basically, you get so many that you couldn't use them all if you tried. Plus, you're allowed out during the week in your C1C year. But if you want exact numbers, I'll let a current cadet chime in with exact passes.
I think I got 6 this semester, but I did some volunteer work and I have already gotten like 8 performance passes between all the community service projects I've participated in. This is my C4C year.