I generally do 6 days on (2x swim, bike, run) and then 1 day off. However, lately I've been trying to do a run every third day so I've been skipping some of my days off to get everything in (no double workout days yet). I actually went all of February without a day off (plus 2 more weeks of March), but a few of the days were pilates or stretching and nothing else. I've been holding up well, but I wouldn't recommend it.