How Often Should I CrossFit?

Well that's easy: it depends.

Many factors may contribute to how often you choose to CrossFit including rest, nutrition, current level of fitness, and goals. Of course your work/home/kids schedule will also be a part of which days you choose workout and which you will rest. 

Here's a link to a great article by CrossFit Impulse that gives a short version and a long version of the answer.