Ann Graybiel of MIT’s McGovern Institute has shown through research that neurons change their firing patterns when habits are learned, and then change them again when unlearned. However, as soon as something kicks back in the habit, they are fired back up.  That is why it is so easy to pick back up negative addictions like smoking and drinking, but also why if you establish good habits but lose them, you can kick them back up much easier as well.

So how long does it take to establish habits?  While the well established rule on habits is 21-28 days, the UK Health Behaviore Research Centre recently came out with research that found it took 66 days to form a habit.   I would tend to agree with the latest research — if we can do something for 66 days straight, we can do it for a year, five, or thirty.  21 or 28 days seems to be just enough time to make it questionable, or make you confident but not be able to stick to it.

It is sad to learn that we keep the pathways forever when we think in terms of addictions, but it is also great to know that we keep these pathways forever if we have healthy habits like meditation and working out.  I don’t know what research is the ‘correct’ research, but I would argue 21 days to develop a bad habit, 66 to develop a good one to be on the safe side.

Source: http://blogs.psychcentral.com/adhd/2010/05/how-long-does-it-take-an-action-to-become-a-habit-21-28-or-66-days/