How Long Does It Take to Form a Habit? Not 21 Days, and That's Good News

Somewhere around the second week of January, a lot of us start doing math. Okay, I've hit the gym nine days in a row. Twelve more and it's a habit, right?

The 21-day rule is one of the most repeated ideas in self improvement. It's on posters, in apps, in an alarming number of LinkedIn posts. It also isn't true, at least not the way it's usually told. The good news is that the real answer is more forgiving than the myth, and once you know it, you can stop quitting on day 22 because nothing magical happened.

Where the 21-day idea came from

The number traces back to Maxwell Maltz, a plastic surgeon who published a bestselling book called Psycho-Cybernetics in 1960. Maltz noticed that his patients seemed to take a few weeks to get used to their new faces, and that amputees took a while to stop feeling a phantom limb. He wrote that it "requires a minimum of about 21 days for an old mental image to dissolve and a new one to jell."

Look at the words he chose. Minimum. About. He was describing something he'd observed in his practice, not reporting an experiment about habits. Over the next few decades the hedges fell off, the context fell off, and "a minimum of about 21 days to adjust to a new self-image" turned into "21 days to form a habit." It's a great example of how a claim gets more confident the further it travels from its source.

What the research actually found

The study most people cite now was published in 2010 by Phillippa Lally and her colleagues at University College London, in the European Journal of Social Psychology. They recruited 96 people and asked each one to pick a single new daily behavior tied to something they already did. Eat a piece of fruit with lunch. Drink a bottle of water after breakfast. Do 50 sit-ups before dinner. Every day, participants reported how automatic the behavior felt, using questions like "I do it without thinking."

Three findings are worth knowing.

It took around 66 days on average. That's how long it took, for the typical participant, for automaticity to level off. Not three weeks. More like two months.

The range was enormous. Some people got there in 18 days. For others, the researchers projected it would take as long as 254 days. That top number is an extrapolation, because the study only ran 84 days, but the spread is the point. Drinking a glass of water is not the same project as doing 50 sit-ups, and you are not the same person as your coworker.

Missing one day didn't wreck anything. A single missed repetition had little effect on how the habit developed. Missing a lot of days did slow things down. But the all-or-nothing thinking that makes people quit after one bad Tuesday wasn't supported by the data.

It's also fair to say what this study isn't. It's one study, with a modest sample, relying on people's own ratings of how automatic something felt. It's a good study, and it changed how researchers talk about habits, but it's not a law of nature. "About two months, give or take a lot" is the honest summary.

Why the real answer is better news

At first, 66 days sounds worse than 21. Three times worse, actually.

But think about what the 21-day myth does to people in practice. You push hard for three weeks, waiting for the switch to flip. On day 23 the gym still feels like a chore, and you conclude that you're the problem. You must not have the discipline gene. So you stop.

The real research says something kinder: it's supposed to still feel effortful at three weeks. You're not broken. You're in the middle. And if you miss a day because your kid got sick or the Thanksgiving travel was a nightmare, you haven't reset to zero. You just pick it back up.

Marcus Aurelius, the Roman emperor who kept a private notebook that we now call the Meditations, put the underlying idea better than any app. In our English translation (Meditations 5.16):

As your repeated impressions are, so will your mind be; for the soul is dyed by its impressions.

Dyed is the perfect verb. You don't dye fabric by dipping it once. You soak it, again and again, and the color deepens a little each time. Some days it barely seems to take. Then one day you notice it's just the color of the cloth now.

How to build a habit that sticks

Here's what the research suggests, translated into plain steps.

1. Make it embarrassingly small. The behaviors that became automatic fastest in Lally's study tended to be simple ones, like drinking water. If your goal is "work out for an hour," your daily habit could be "put on gym clothes after I get home." You can always do more. The habit is the part you do even on bad days.

2. Hook it to something you already do. Every participant picked a cue, like after breakfast or before dinner. Habits are, at bottom, links between a situation and an action. "After I start the coffee maker, I read one page" gives your brain a hook to hang the new behavior on. Vague intentions like "read more" have no hook.

3. Keep the context steady. Same time, same place, same trigger, at least at first. That's why a morning habit is often easier than a "whenever I get a chance" habit. Whenever never comes.

4. Forgive the gap, not the pattern. Missing one day is noise. Missing three in a row is a pattern starting to form, and that's when it's worth asking what changed. Did the cue disappear? Did the habit get too big?

5. Expect the boring middle. Somewhere between week three and week eight, the novelty is gone and the automaticity hasn't arrived yet. This is the stretch the 21-day myth tells you shouldn't exist. It does. Plan for it. Make the habit even smaller during this stretch if you need to. The goal is to keep the chain alive, not to make it impressive.

6. Track it, lightly. A paper calendar with checkmarks is enough. Seeing a run of marks is motivating. Seeing one gap in a long run is also useful, because it shows you that one gap didn't end anything.

What a habit buys you

There's a passage in Hermann Hesse's Siddhartha where the young hero, who has nothing, is asked what he can offer. He answers with three skills: "I can think. I can wait. I can fast." It sounds like nothing. It turns out to be everything, because those three abilities let him walk into a new life without being pushed around by hunger or impatience.

Habits work the same way. The point isn't the sit-ups or the fruit at lunch. It's that once something is automatic, it stops costing you willpower, and you get to spend that willpower somewhere else. A reading habit, for instance, is mostly the habit of opening the book. The rest takes care of itself. (If that's the habit you're after, we wrote a whole plan in how to read more books.)

So pick one small thing. Tie it to something you already do. Expect about two months, give or take a lot. And if you miss a day, don't start over. Just continue.

Both books quoted here are in the Ether Library in our new English translations: Siddhartha and the Meditations.

Sources

• Phillippa Lally, Cornelia H. M. van Jaarsveld, Henry W. W. Potts, Jane Wardle, "How are habits formed: Modelling habit formation in the real world," European Journal of Social Psychology, 2010. Summary: British Psychological Society Research Digest, "How to form a habit": https://bps.org.uk/research-digest/how-form-habit
• James Clear, "How Long Does it Actually Take to Form a New Habit? (Backed by Science)" (on Maltz's original wording): https://jamesclear.com/new-habit
• Marcus Aurelius, Meditations, 5.16, quoted from the Ether Library English translation.
• Hermann Hesse, Siddhartha (1922), quoted from the Ether Library English translation.