How Long Does It Take to Form a Habit? The 'Three-Week' Rule

By: Julia Layton  | 
Habits build well-worn synaptic pathways in our brains.

Anyone who's ever tried to start an exercise routine, quit smoking or change a sleep pattern knows how powerful a habit can be. Habits seem to be more than behaviors — they seem to be part of who we are.

Habits are essentially patterns of behavior that become "worn in" to our brains. Someone who wakes up every morning, pours a cup of coffee and lights a cigarette, in that order, every morning, has that pattern built into their brain, in the form of well-used synaptic pathways. But how long does it take to form a habit?


In this article, we'll find out whether you really can turn a new behavior into a habitual one by repeating it for 21 days — a number often cited as the key to forming a new habit. We'll see where the belief originates and whether there's any hard evidence to back it up.

To understand what goes into forming or breaking a real habit, and how long that might take, it's helpful to look at what goes on in the brain once pattern-enforcing synaptic pathways are "worn in."


Firing Across Synapses

The impulses firing across synapses, or spaces between certain cells that guide communication in the brain, govern everything we do (and think, for that matter). When we repeat any behavior or pattern enough, the synaptic pathways associated with that pattern get used to being accessed.

As a result, it becomes easier for impulses to travel along those pathways, and the behavior seems "natural." In other words, to the brain, wake-coffee-cigarette, in that order, is practically instinctive. One action triggers the next.


So when someone tells you, as many self-help gurus might, that the habit formation process occurs in three weeks, it's natural to be skeptical. Why specifically three weeks? And how could you form a new instinctive behavior in such a short period of time?


Habits: Make It and Break It

Most smokers will tell you it takes a lot more than three weeks of mindful thinking to disrupt those synaptic pathways and bad habits.
Photo courtesy of Iowa Department of Administrative Services

No one is entirely sure where the 21-day rule originated, but a book called "Psycho-Cybernetics" seems to have set forth the idea. It's a self-help book first published in the 1970s, and in it, you find out you can create or break a habit in just 21 days.

The problem is, the evidence supporting the theory is empirical, or based on experience, not clinical, or based on controlled experiments [source: Benefit].


The theory caught on, though, and others have backed it up since then. In 1983, for instance, a woman chronicled her journey to create positive habits — namely to start flossing and stop criticizing — in "Three Weeks to a Better Me," an article for Reader's Digest.

But does it really work for everyone, or are these just the experiences of a couple of individuals?

The reality is that it is easier to form a new habit than it is to break bad habits. If you repeat new behaviors often enough, those synaptic pathways are going to get worn in. The human brain is a very adaptive piece of machinery. But does that take 21 days? Who knows? Everyone's brain is different, and habit forming also relies on aspects of experience and personality.

Breaking a habit is a lot more complicated because while parts of those worn-in pathways can weaken without use, they never go away [source: Rae-Dupree]. The slightest provocation can reactivate them [source: Delude]. If you've ever tried to quit smoking, you already know this. You can go a year without a cigarette, and then give in one time and BAM, the habit comes right back.

The best you can do, then, is to form a new, parallel pattern, like exercising when you feel stressed, rather than indulge in the old pattern, which triggers "cigarette" in response to stress.

So what about these 21 days?


How Long to "Habit?"

Making specific plans for achieving goals is a more likely way to successfully make or break habits.
Nick Clements/ Digital Vision/Getty Images

If you've ever tried to break any habit at all, you can get a good feel for the reality of the 21-day rule by examining the following statement made by the "Self Improvement Mentor":

[…] complete abstinence of a habit for 21 to 30 days will be enough to break it. So, you don't have to worry about having to continuously struggle to not indulge in a habit for the rest of your life. After 21 to 30 days, you would have surpassed the required threshold. [source: SIM]

Or in this statement made by the writers of the self-help book "The Secret," referring to a variation of the habit rule that says it takes 30 days:


[…] changing the habit will take 30 days, re-affirming it further for another 30 days will definitely fix it and you'll have no problem to continue from there on. [source: Secret]

Wow, really?

Changing a habit is never that simple. If it were, those struggling with food would have healthy habits, alcoholics would never relapse, and everyone would adhere to a healthy diet 100 percent of the time.

For most people, staying away from a bad habit is a lifetime effort, backed up by the fact that those well-worn synaptic pathways never go away. There's no apparent scientific reason why it would take three weeks to break an old habit or make a new habit.

Depending on your unique physical and mental health, it could take a few weeks, it could take five days or it could take nine months.


How to Make a New Habit and Break a Bad Habit

Building habits is not easy, but there are some steps you can take to increase your chances of success in the endeavor, including:

  • Take small steps. Don't try to do everything at once. So instead of "I'm going to exercise every day," start with "I'm going to exercise twice a week."
  • Only try to change one habit at a time. Instead of "I'm going to quit eating junk food, start exercising and go to sleep at 10 p.m. instead of 2 a.m.," start with "I'm going to quit eating junk food."
  • Write down the habit you want to change and be specific. Rather than writing "I will exercise," write, "I will start walking 30 minutes, twice a week, on Monday and Thursday, and I will wake up at 7 a.m., so I can walk before work on those days."
  • Repeat the behavior you're aiming for as often as you can. The more you repeat a behavior, the more likely it is that it will become "instinctive."

[source: Newby-Clark]



Frequently Answered Questions

Who said it takes 21 days to form a habit?
While there's no definitive answer on who first said that forming habits takes 21 days, Maxwell Maltz, a plastic surgeon, wrote about it in his 1960 book, "Psycho-Cybernetics."

Lots More Information

Related HowStuffWorks Articles

  • Benefit, Ariane, M.S.Ed. "Mythbusting: Are New Habits Established in 21 Days?" Neat & Simple Living. June 20, 2007.
  • Delude, Cathryn M. "Brain researchers explain why old habits die hard." MIT News. Oct. 19, 2005.
  • Discipline: 30 Days to Form a New Habit. The Secret.
  • The Essence Of Habit Formation. Self Improvement Mentor.
  • Graybiel, AM. "Habits, rituals and the evaluative brain." Annu Rev Neurosci. 2008;31:359-87. PubMed.
  • Ludington, Aileen, MD. "Habit formation: How to change." The Quiet Hour.
  • Newby-Clark, Ian. "Five Things You Need to Know About Effective Habit Change." ZenHabits.
  • Rae-Dupree, Janet. "Can You Become a Creature of New Habits?" The New York Times. May 4, 2008.
  • Tips on how to break a habit. Self Improvement Mentor.