To know how often you should take a juice cleanse, you need to know the prime motive for going on one. A juice cleanse is done to reboot your health and push out the toxins from your body. If you follow an active lifestyle and a healthy diet, once in three months would be more than enough.
But if you are a fan of junk food and you feel your energy is low all the time, it's highly recommended to follow a juice fast once a month, and it should last for a minimum of 2 days. This way, you are pushing out the toxins as and when they come your way and not waiting for them to pile up.