How long did it actually take for people to form a habit? Dean writes:In a study carried out at University College London, 96 participants were asked to choose an everyday behavior that they wanted to turn into a habit. They all chose something they didn't already do that could be repeated every day; many were health-related: people chose things like "eating a piece of fruit with lunch" and "running for 15 minutes after dinner." Each of the 84 days of the study, they logged into a website and reported whether or not they'd carried out the behavior, as well as how automatic the behavior had felt.
The simple answer is that, on average, across the participants who provided enough data, it took 66 days until a habit was formed. As you might imagine, there was considerable variation in how long habits took to form depending on what people tried to do.
It's like trying to run up a hill that starts out steep and gradually levels off. At the start you're making great progress upwards, but the closer you get to the peak, the smaller the gains in altitude with each step.
While the finding may at first appear disheartening, it's actually oddly assuring in reminding us that habit, like genius, is merely a matter of doggedness and "deliberate practice" – in fact, this brings us to the lesser-cited yet pivotal second half of Aristotle's famous dictum:"Excellence … is not an act but a habit."Although the study only covered 84 days, by extrapolating the curves, it turned out that some of the habits could have taken around 254 days to form – the better part of a year!What this research suggests is that 21 days to form a habit is probably right, as long as all you want to do is drink a glass of water after breakfast. Anything harder is likely to take longer to become a really strong habit, and, in the case of some activities, much longer.