How ofter do you take a day off?

Whenever I need one, which is usually every 16 to 21 days. I do have one or two unload (easy) days every week... for most of the athletes I coach I schedule one day off a week more as a mental rest and/or a day they can have for personal life priorities and not necessarily because they need it.

Once a week is generally good for me. But more as the body demands them.

And rest days for me generally include yardwork and walking.  

Define "off" day.  For some people, an off day is an easy day or only one activity.  For others, it's completely off, no structured exercise.

By plan, one day week.  With a wife and kids and a household to maintain, it often turns in to an "active rest day"--doing yardwork, moving furniture, doing sports with the kids.

I find that I usually average one unplanned rest day each month (by listening to my body). 

I had to take more when I was first ramping up to five two-a-days per week, but I think now I'm adjusted.

Also, every 4th or 5th week, I incorporate a Recovery Week--meaning half-volumes or less for the entire week.