Chances are that you have heard the wisdom that it takes 21 days to form a new habit. It's a comforting thought. "Who wouldn't like the idea of changing your life in just three weeks?" asks James Clear at the Huffington Post. Unfortunately, it's also just not true. Clear traces the history of the myth back to a 1960 book by plastic surgeon Maxwell Maltz, who observed that it tended to take patients at least 21 days to adjust to their new faces and other bodily changes—the key words being "at least." Over time, those words fell away and "21 days" gained fame as the hard-and-fast rule.
So how long does it really take? Clear dug up a 2009 study in which researchers followed 96 people as they tried to adopt new habits (example: drinking a bottle of water with lunch). The results? Subjects reported behaviors becoming automatic in an average of 66 days. For some it took as little as 18, but for others it stretched as long as 254. Bottom line: Building habits takes time. "All the '21 Days' hype can make it really easy to think, 'Oh, I'll just do this and it'll be done,'" Clear writes. But "habits are a process, not an event."