New Year’s resolutions are a ritual of bold promises that rarely stand the test of time. A Forbes Health survey of 1,000 respondents revealed that 48% aimed to improve their fitness, 38% focused on improving finances, 36% targeted better mental health, and 34% set out to lose weight. Yet when asked how long they maintained previous resolutions, only 8% persisted for one month and just 1% for an entire year.
This striking data encapsulates a familiar cycle: the surge of optimism on New Year’s Eve soon gives way to fading resolve, creating a pattern of renewed ambition followed by inevitable setbacks. Instead of attributing these failures to a lack of personal determination, the discussion here challenges a common myth about habit formation and explores what truly underpins long-term behavioral change
The Myth of 21 Days
It was once believed that a habit forms after 21 consecutive days—a notion popularized by surgeon and writer Maxwell Maltz in “Psycho-Cybernetics: A New Way to Get More Living Out of Life.”
Despite its serious-sounding title, the book is essentially a self-help work that flirts with fiction. Maltz explores his views on self-image, linking them to fields such as physics, anatomy, and cybernetics - the study of regulation and control, particularly how information flows and is used for self-regulation. Achieving goals was simply a matter of changing one’s self-perception; a “change of mindset” and positive thinking were sufficient—any resemblance to health coach rhetoric is not coincidental.
Maltz developed this theory after noticing that patients undergoing facial plastic surgery took about 21 days to adjust to their new appearance. He also observed similar patterns in other contexts, such as couples feeling more comfortable in a new home after three weeks or amputee patients experiencing phantom limb syndrome [1] for roughly the same period.
From these rather anecdotal observations, Maltz proposed that it takes a minimum of 21 days for an old mental image to dissolve and be replaced by a new one. Maltz's conclusions, based solely on his clinical observations, not rigorous clinical trials or cohort studies, made his claims scientifically unsound. Despite this, his hypothesis has been widely extrapolated, even evolving into the claim that it takes 90 days to establish a lifestyle.
How Are Habits Formed?
While the public often uses habit synonymously with habitual or frequent behavior, in psychology, it has a more specific definition: an action triggered automatically in response to contextual cues.
Research shows that repeating a simple action in a stable context can, through associative learning, make the behavior automatic. This reduces the need for conscious effort and frees up mental resources. For example, volunteers aiming to lose weight developed automatic physical activity or dietary habits through consistent repetition, making initially challenging behaviors feel natural.
An article in the British Journal of General Practice reviewed the psychology behind habit formation and suggested that healthcare professionals encourage patients by providing advice tailored to our intuitive, automatic thinking that requires very little effort and operates without conscious voluntary control.
Based on these findings, the authors propose a three-phase approach:
Initiation Phase: Defining the behavior and the context in which it will occur. Individuals must be motivated to choose a goal they want to achieve; selecting an appropriate context—such as linking the behavior to a daily event ("after I finish my coffee") or a specific time reinforces the association between the action and its cue. Small, manageable changes help prevent discouragement and facilitate long-term success.
Learning Phase: Repeatedly performing the behavior in the chosen context strengthens the association between the stimulus and the action, gradually leading to automaticity. Consistent repetition and persistence transform an intentional behavior into a habit.
Stability Phase: Once automaticity develops, the habit becomes “ingrained” and requires minimal effort to maintain.
Habit formation was also explored in the review article Promoting habit formation where the authors’ conclusions converge with previous research while highlighting two additional points:
- The “intention-behavior gap” reflects the discrepancy between what is planned and what is actually executed. It can be overcome by self-regulation strategies such as planning.
- Rewards can lead to contradictory outcomes. For example, intrinsic rewards (e.g., pleasure and satisfaction) generally facilitate habit formation, while extrinsic rewards (e.g., financial incentives) yield inconsistent results. Some studies even suggest that extrinsic rewards may hinder habit formation if they become the primary focus.
Even complex behaviors can eventually become automatic through consistent repetition, albeit at a slower pace. Furthermore, if you miss a day or experience an occasional lapse, don’t worry; these setbacks have little impact in the long run.
Finally, in some cases, establishing a new healthy habit often involves replacing or eliminating an undesirable one. This can be achieved by avoiding the triggers of the old behavior or, when avoidance isn't feasible, by employing strategies to identify and control triggers that link new behaviors to specific cues.
How Many Days Until a Habit Forms?
One of the first rigorous studies on habit formation was published in the European Journal of Social Psychology. In this study, researchers investigated how automaticity develops when individuals establish new habits.
96 university students were asked to adopt a new habit related to healthy eating, drinking, or exercise that met the following three criteria:
- It could not be a behavior they already practiced.
- It must be linked to an identifiable daily event (stimulus).
- The stimulus had to occur once per day to ensure consistency.
Some examples included “eating a piece of fruit at lunch,” “running for 15 minutes before dinner,” and “drinking a bottle of water with lunch.”
Participants were instructed to perform their chosen behavior daily for 84 days and report their progress on a study website. They also completed a modified Habit Self-Report Index (HAI), a tool designed to measure habit strength based on factors like repetition history, identity expression, and automaticity.
The final analysis included 39 participants, classified as having “adequate adherence” to the study model.
The results showed that:
- Automaticity plateaued at 66 days, with individual variation ranging from 18 to 254 days.
- Developing an exercise habit took 1.5 times longer than establishing eating or drinking habits. The median time was 65 days for eating, 59 days for drinking, and 91 days for exercise.
- Initial repetitions produced greater automaticity than later ones, indicating diminishing returns. Missing a single day resulted in only a minor, temporary drop in automaticity.
- Nearly half of the motivated participants did not practice their chosen behavior consistently enough to form a habit.
Despite the small sample size and the reliance on self-reported data, the findings indicate that consistently repeating a behavior in a stable context gradually strengthens automaticity, underscoring the importance of repetition in habit formation. There were no extrinsic rewards, suggesting they are unnecessary, especially when replaced by intrinsic motivation.
A recent systematic review and meta-analysis examined the time necessary to develop healthy habits and what factors, such as environmental conditions and individual characteristics, affect this process.
Sixteen articles met the inclusion criteria, analyzing data from 2,601 participants, in studies with sample sizes ranging from 20 to 537. The most commonly studied habits included exercise, dietary changes, and flossing. Habit formation times ranged from 2 to 5 months, with some studies finding rapid initial gains that plateaued, while others showed gradual increases over more than a month, highlighting the complex interplay of psychological, behavioral, and contextual factors.
The review emphasized the need for long-term interventions and ongoing professional support to sustain behavioral changes.
As we can see, creating and maintaining a habit isn’t solely about willpower; it requires strategies that simplify execution and seamlessly integrate the behavior into daily life. Taking anywhere from 4 days to nearly a year, habit formation isn’t a one-size-fits-all timeline—it’s a slow grind of repetition, context, and, most importantly, realistic expectations. I’m confident that by 2026, I’ll be shredding violin solos like Eddie Berg, lead singer of Imminence. Even if that doesn’t happen, I’ll have at least picked up the damn thing and learned to play a few songs.
[1] Phantom limb syndrome is a condition in which patients experience sensations in an amputated limb, which may be painful or not.
Source: Making health habitual: the psychology of ‘habit-formation’ and general practice. Br J Gen Pract. DOI: 10.3399/bjgp12X659466
How are habits formed: Modelling habit formation in the real world. Eur. J. Soc. Psychol. DOI: https://doi.org/10.1002/ejsp.674
Time to Form a Habit: A Systematic Review and Metan-Analysis of Health Behaviour Habit Formation and Its Determinants. Healthcare. DOI: 10.3390/healthcare12232488
