How Long Does it Take to Form a Habit? 21 Days? 66 Days?

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Making health habitual: the psychology of ‘habit-formation’ and general practice

ADDRESS FOR CORRESPONDENCE Benjamin Gardner Health Behaviour Research Centre, Department of Epidemiology and Public Health, University College London, Gower Street, London, WC1E 6BT, UK. E-mail: [email protected]

Patients trust health professionals as a source of advice on ‘lifestyle’ (that is, behaviour) change, and brief opportunistic advice can be effective. 2 However, many health professionals shy away from giving advice on modifying behaviour because they find traditional behaviour change strategies time-consuming to explain and difficult for the patient to implement. 2 Furthermore, even when patients successfully initiate the recommended changes, the gains are often transient 3 because few of the traditional behaviour change strategies have built-in mechanisms for maintenance.

Brief advice is usually based on advising patients on what to change and why (for example, reducing saturated fat intake to reduce the risk of heart attack). Psychologically, such advice is designed to engage conscious deliberative motivational processes, which Kahneman terms ‘slow’ or ‘System 2’ processes. 4 However, the effects are typically short-lived because motivation and attention wane. Brief advice on how to change, engaging automatic (‘System 1’) processes, may offer a valuable alternative with potential for long-term impact.

Opportunistic health behaviour advice must be easy for health professionals to give and easy for patients to implement to fit into routine health care. We propose that simple advice on how to make healthy actions into habits — externally-triggered automatic responses to frequently encountered contexts — offers a useful option in the behaviour change toolkit. Advice for creating habits is easy for clinicians to deliver and easy for patients to implement: repeat a chosen behaviour in the same context, until it becomes automatic and effortless.


While often used as a synonym for frequent or customary behaviour in everyday parlance, within psychology, ‘habits’ are defined as actions that are triggered automatically in response to contextual cues that have been associated with their performance: 5 , 6 for example, automatically washing hands (action) after using the toilet (contextual cue), or putting on a seatbelt (action) after getting into the car (contextual cue). Decades of psychological research consistently show that mere repetition of a simple action in a consistent context leads, through associative learning, to the action being activated upon subsequent exposure to those contextual cues (that is, habitually). 7 – 9 Once initiation of the action is ‘transferred’ to external cues, dependence on conscious attention or motivational processes is reduced. 10 Therefore habits are likely to persist even after conscious motivation or interest dissipates. 11 Habits are also cognitively efficient, because the automation of common actions frees mental resources for other tasks.

A growing literature demonstrates the relevance of habit-formation principles to health. 12 , 13 Participants in one study repeated a self-chosen health-promoting behaviour (for example, eat fruit, go for a walk) in response to a single, once-daily cue in their own environment (such as, after breakfast). Daily ratings of the subjective automaticity of the behaviour (that is, habit strength) showed an asymptotic increase, with an initial acceleration that slowed to a plateau after an average of 66 days. 9 Missing the occasional opportunity to perform the behaviour did not seriously impair the habit formation process: automaticity gains soon resumed after one missed performance. 9 Automaticity strength peaked more quickly for simple actions (for example, drinking water) than for more elaborate routines (for example, doing 50 sit-ups).

Habit-formation advice, paired with a ‘small changes’ approach, has been tested as a behaviour change strategy. 14 , 15 In one study, volunteers wanting to lose weight were randomised to a habit-based intervention, based on a brief leaflet listing 10 simple diet and activity behaviours and encouraging context-dependent repetition, or a no-treatment waiting list control. After 8 weeks, the intervention group had lost 2 kg compared with 0.4 kg in the control group. At 32 weeks, completers in the intervention group had lost an average of 3.8 kg. 14 Qualitative interview data indicated that automaticity had developed: behaviours became ‘second nature’, ‘worming their way into your brain’ so that participants ‘felt quite strange’ if they did not do them. 10 Actions that were initially difficult to stick to became easier to maintain. A randomised controlled trial is underway to test the efficacy of this intervention where delivered in a primary care setting to a larger sample, over a 24-month follow-up period. 16 Nonetheless, these early results indicate that habit-forming processes transfer to the everyday environment, and suggest that habit-formation advice offers an innovative technique for promoting long-term behaviour change. 13

Does It Take Just 21 Days to Form a Habit?

Let’s jump back 60 years to 1960, when Dr. Maxwell Maltz wrote the book Psycho-Cybernetics. Dr. Maltz was a plastic surgeon at the time who had a passion for helping other people improve their self-image. He is also one of the first recognized authors in the self-help book genre.

In his book, Dr. Maltz shared his observation that it took a minimum of about three weeks (on average) for his surgical patients to let go of their pre-surgical perceptions of themselves and become accustomed to their new appearance.

Dr. Maltz said it typically took at least 21 days for his patients to accept their appearances–not at most or exactly. And he said this based upon his own observations, not facts or scientific research.

But It’s easy to see why and how this myth could spread. The time frame is easy to remember, and it’s just short enough to help people think they can get through it, but still long enough to seem plausible. And doesn’t everyone want to make a significant change in their life in under a month?

So How Long Does it Actually Take to Form a Habit?

In the aforementioned study (and you can read the entire study here), Phillippa Lally, alongside three other researchers, dug deep into this question. Here are some key points to their study of the process of everyday habit formation:

  • 96 volunteers chose a specific behavior to carry out every day under the same circumstances (such as ‘after breakfast’) for 12 weeks.
  • The volunteers completed a self-reported habit index worksheet each day to record whether or not they did their chosen behavior.
  • Out of the 96 volunteers, 39 performed their habit with enough consistency to qualify to be considered for the results of the study (i.e. those who only carried through with the behavior once a week were discounted from the study).
  • It took participants between 18 and 254 days for their behavior to become automatic enough that they would perform it without thinking about it first.
  • These findings show there is a wide variation in how long it could take you to form a habit.
  • *It is true that this study ran for only 84 days, but the researchers used the data they gathered to make an informed statistical estimate regarding the longer timelines (254 days) to integrate new habits into one’s life. Remember, the exact number of days is dependent on many factors and isn’t as important as the general findings of this study, which are that habits can take a really long time to stick.



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