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How Many Days Does It Take To Form A Habit? ‘Not 21,’ Science Says.

How many days does it take to form a habit? Many ‘experts’ will tell you it takes 21 days. That’s not what the science says though.

How Many Days Does It Take To Form A Habit? ‘Not 21,’ Science Says.

The next time I hear that it takes 21 days to form a habit I’m going to shoot myself.

Well, not really, I value my life more than that, but it’s still painful to hear the same misconception over and over and over.

Before we dive into how long it really to form a habit let’s discuss:

Why should you even care about habits? What does it mean to make something a habit?

Habit is a behavior you do recurrently and almost unconsciously. You literally just do it.

Driving is a great example. You open the door for your dog automatically. You put your seatbelt on without even thinking about it. Then you drive to your best friend’s house while you think about everything else in the universe other than your route, or whether you should change gears, or how to take a turn.

form a habit

You’ve driven enough and done this particular route so many times that all this is ridiculously easy to you. So easy you have the luxury to put your mind elsewhere.

Now here’s where it gets really interesting.

Because a habit is second nature, it feels uncomfortable when you don’t do it.

Say you have the habit of eating ice-cream when you’re sad. Ever tried to stop yourself from comfort eating? How did it feel? Maybe your desire for cookies intensified?

Now ever heard of people who exercise regularly say things like their body complaining if they miss a workout and can’t get back to yoga/the gym/whatever it is they’re doing? (Or are you one of them?)

It’s the habit kicking in. And it shows why forming good habits can be such a game changer: You’ll be naturally inclined to do things that are good for you, and even if something gets in the way this will only intensify your desire to make it happen.

Now back to the 21-day rule.

Does the 21-day rule to form a habit even make sense?

Before we get into the details on how this became popular, let’s first sharpen our critical thinking skills.

Here’s the loophole I see right away: What is meant by a habit? Make what type of behavior a habit?

Because surely going from 7 to 8 glasses of water a day is going to be different than going from 3 to 8. And both of those will feel different when switching from waking up at 9 am to waking up at 8 am.

And again all of those will be different if trying to replace your cookie comfort-eating habit with carrots (sounds like a bad idea, don’t even try this.)

So what exactly are we supposed to form into a habit? Doesn’t it only make sense that the time it takes to form a habit will depend on:

  • the difficulty of the new activity
  • whether the activity is something we do once a day, more or less frequently
  • how easy it is to practice the activity
  • how happy this new activity makes us (surely forming the habit of eating chocolate daily will be easier than waking up 2 hours earlier)

And now that I’ve pointed the red flags about this bogus rule let’s examine where it actually comes from.

So where does the 21-day rule to form a habit come from and why is it so popular?

A lot of people will tell you it takes 21 days to ingrain a habit, and it has become somewhat dogma in the world of behavior change, psychology, and self-help.

Is this 21 day rule based on science though? An equation formulated by some Einstein-esque mathematician? Or the opinion of expert researchers in the psychology field?

Nope; not even close.

In fact, this whole theory stems from the work of Dr. Maxwell Maltz; a plastic surgeon come best-selling author who wrote about observations he had made from his own experiences and that of his patients after their surgery.

In his book ‘Psycho-Cybernetics’ (4), Maltz states:

“Following plastic surgery it takes about 21 days for the average patient to get used to his new face.”

“When an arm or leg is amputated the “phantom limb” persists for about 21 days”

“People must live in a new house for about three weeks before it begins to “seem like home.””

Following these observations, Maltz went on to conclude that it takes a minimum of 21 days for a new habit to develop.

“These, and many other commonly observed phenomena tend to show that it requires a minimum of about 21 days for an old mental image to dissolve and a new one to jell.”

I’ve put emphasis on ‘minimum’ because much like a dodgy game of Chinese whispers, this all got muddled up and gave birth to the myth that 21 is the golden number of days it takes to develop a habit.

And just like that, we have the 21 day rule of habit development.

When you dig into the science, it paints a different picture though, and in reality just like I’ve pointed in the loopholes above, there’s much more to it than the 21 day rule suggests.

So how fast can you form a new habit?

how long to form a new habit

Not all habits are created equal and the time it takes for a behavior to become a habit will depend on a multitude of different factors, including:

  • complexity of the new activity
  • how it fits in your routine
  • how often you practice it
  • individual differences

Let’s review those one by one.

How many days does it take to form a habit? Complexity matters.

Just think about this for a sec; which of the two would you find easier to engrain:

1. Drinking a glass of water with breakfast in the morning


2. Going for an hour long run moments after you roll out of bed


Yeah, that’s what I thought; the water.

So the complexity of the behaviour matters. In other words, a behaviour that can be broken down into lots of components (e.g., going for a run) takes longer to become autonomous than one that’s made up of fewer components (eg: drinking water with breakfast) (5).

It’s not just me saying this either; there is science to support it too.

  • In 2006, Verplanken (6) gave students one of two writing tasks. The first group simply had to underline ‘She/she’ every time they came across it in a piece of text. The other group had the more complex task to underline all words referencing a moveable object or mammal. What they found was that the simple task became more autonomous by the end of the study, indicating that they’re quicker/easier to become habitual.
  • A little more recently, Lally et al., (2) recruited students to choose a health related behaviour they wanted to develop into a habit. The students chose behaviours like doing 50 sit ups with their morning coffee, eating a piece of fruit with lunch, and drinking a glass of water with their lunch. What they found was that developing an exercise habit took one and a half times longer than an eating or drinking habit, which they suggested was because the eating/drinking behaviors were much simpler than the exercise ones.

In a practical sense, this means you need more commitment initially for complex behaviours like getting involved in that gym class you’ve been promising yourself you’d start doing months ago.

Why? Because you’ll have to stick at it longer before you start doing it without thinking.

How many days does it take to form a habit? It depends on how it fits into your routine

It doesn’t just come down to the complexity of the behaviour either though, and more finite details like how the behaviour fits in with other lifestyle factors and routines can impact how long it takes to become a habit.

This was shown in a study by Judah et al., (5) who looked into the development of flossing habits. They had two groups: one was instructed to floss after cleaning their teeth, and the other group was told to floss between getting out of the shower and cleaning their teeth.

They found that after 8 months, the latter group had poorer flossing habits, which they thought was because the flossing was sandwiched between two existing habits (showering, then cleaning teeth). This meant that it didn’t just require the development of a new habit (flossing), but the disruption of previously interlinked ones too.

So if a behaviour disrupts your current routine and habits, it’s likely to take longer to become habitual.

How many days does it take to form a habit? It depends on frequency and consistency

It goes without saying that the more frequently and consistently you do something, the sooner it will become autonomous. For example, you can’t expect to pick up a habit like going to the gym if you’re only doing it once every month.

In fact, research by Kaushal and Rhodes (7) suggests it takes at least 4 gym sessions per week for 6 weeks to establish an exercise habit. That doesn’t mean you can’t develop an exercise habit by going less frequently; it just means it will probably take longer for it to become autonomous.

The same goes for other behaviors; the more frequently you do them, the quicker they’re likely to become a habit.

How many days does it take to form a habit? It varies from person to person.

Finally, the same habit is not created equal for us all. Consider the exercise example above; do you think an active, sporty, and naturally athletic person would take the same amount of time to pick up the habit of going to the gym as a sedentary couch potato?

Nope; I didn’t think so.

You see, the sedentary person would likely be more uncomfortable with the thought of stepping foot in an alien-like gym, they may be less confident with their ability to perform exercises, and they might be more intimidated by all the iron pumping weight lifters throwing barbells about.

This would ultimately make them think about the behavior more so than someone else might. Because a behavior has to be done autonomously and with little thought for it to become a habit, that would mean they’re likely to take longer to develop a gym going habit (7).

So there’s individual variation in the time it takes for a behavior to become a habit.

How Many Days Does It Take To Form A Habit Then? Anywhere between 18 days and 8.5 months!

From the above, it should be pretty clear that there isn’t a precise time scale we can put on habit development, and it will depend on a load of factors including its complexity, how it fits in with your routine, and how frequently you do it.

Going back to the Lally study mentioned earlier (2), it took an average (mean) of 66 days for the students involved to develop their chosen health-related habit. There were huge differences between individuals in some cases though, with one student taking as little as 18 days and another predicted to take up to a whopping 254 days; not exactly the 21 days that is so commonly cited.

(To clarify, 254 days is 8.5 months – longer than even the 6-month mark that is also commonly used.)

Not all the habits developed were as strong as one another either, suggesting that some behaviours become more autonomous than others.

So the take home message here is that there’s huge variability both between individuals and behaviours. No habit is the same, nor is the situation it’s being developed in. Therefore, the 21 day rule is well and truly a myth. Given the available research, a more scientific figure would be 66 days. Even that isn’t enough for some though and shouldn’t be considered the definitive answer by any means.

So you shouldn’t get hung up on a specific time period; rather, you should accept that it’s likely to take much longer than 21 days for things to become autonomous, and focus on consistency to develop your desired habit.

So what habit have you been meaning to build but have not managed to make it happen? What habit have you built successfully? Leave a comment and let me know.


Click here to view the sources referenced in this article.