- Why Does Habit Formation Time Vary?
- The Verdict: How Long Should You Expect?
“It takes 21 days to form a habit.” You’ve probably heard this popular claim, often repeated in self-help books and social media posts. The idea that you can lock in a new habit in just three weeks is certainly appealing – after all, who wouldn’t want to transform their life in a matter of days? But is it true? Where did this 21-day rule come from, and what does scientific research say about the real timeline of habit formation? In recent years, another number has gained fame: 66 days. This comes from a 2009 study suggesting an average of 66 days for habit formation, and it’s frequently cited as the “magic” length of time needed to build a lasting habit. So, which is it – 21 days, 66 days, or something else entirely?
In this article, we’ll debunk the 21-day myth, explore what studies have found about how long habits really take to form, and discuss why the timeline can vary so much. More importantly, we’ll talk about what this means for you: how to stay motivated during the habit-forming period and why focusing on the process, rather than an exact number of days, is the key to success. The Origin of the 21-Day Myth The notion that 21 days is all it takes to form a habit can be traced back not to a scientific study, but to a 1960 self-help book called Psycho-Cybernetics by Dr. Maxwell Maltz. Maltz was a plastic surgeon who observed that his patients typically took about three weeks (21 days) to adjust to changes such as a new nose job or an amputated limb. He also reflected on his own life changes and noted it took around 21 days to form a new personal habit. In his book, Maltz wrote that “it requires a minimum of about 21 days for an old mental image to dissolve and a new one to jell”.
Importantly, Maltz said “a minimum of about 21 days” – but as his anecdotal observation spread through the self-improvement world, that nuance got lost. Over the decades, motivational speakers and authors like Zig Ziglar and Tony Robbins repeated the story. In a classic game of telephone, “a minimum of about 21 days” morphed into a confident assertion that “it takes 21 days to form a habit”. The idea stuck because it’s simple, catchy, and encouraging – three weeks feels doable, yet significant enough to believe. However, it’s crucial to recognize that Maltz’s 21-day timeframe was not based on rigorous scientific research, and it wasn’t even specifically about habit formation in the way we think of habits (it was about adjusting to life changes). It became a widely perpetuated myth because it was repeated so often that people assumed it was fact. As one writer quipped, “If enough people say something enough times, everyone else starts to believe it.”.
What Science Really Says: The 66-Day Average (and Beyond) It took nearly half a century after Maltz’s book for researchers to formally investigate how long habit formation actually takes. The hallmark study on this topic was conducted by health psychology researcher Phillippa Lally and her colleagues at University College London, published in 2009 in the European Journal of Social Psychology. In Lally’s study, 96 participants were each asked to choose a simple health-related habit (such as “eat a piece of fruit with lunch” or “do a 15-minute run in the evening”) and practice it daily for 12 weeks. Each day, the participants reported whether they did the behavior and how automatic it felt. The researchers then analyzed the data to see when the behavior reached a plateau of automaticity – essentially, when it felt more or less effortless or ingrained.
The results: - The time to form a habit varied widely between individuals and behaviors. On the low end, one person formed a habit in just 18 days, and on the high end another person was estimated to take days (about.5 months) – and in fact, some people still hadn’t reached full automaticity by the end of the 12-week study. - On average, across all participants and habits, the time to reach habit automaticity was about 66 days (approximately 2 months and a week). - The type of habit made a difference. Simpler habits were acquired more quickly than more complex ones. For example, a habit like drinking a glass of water after breakfast might become automatic in a few weeks, whereas a habit like doing 50 sit-ups each morning could take many more months to truly stick. - Missing a day here or there did not drastically set back the process. Lally noted that if participants skipped the habit occasionally, it didn’t ruin the overall habit formation – the trend toward automaticity continued as long as they resumed practicing. In other words, perfect consistency wasn’t required, which is a relief for those of us who aren’t perfectly disciplined every single day.
So, 66 days became known as a more evidence-based rule of thumb for habit formation, instead of 21 days. However, even Lally’s study is just an average and an approximation. The authors themselves emphasized that there is no single magic number; the time frame depends on many factors such as the person, the behavior, circumstances, and even things like how rewarding the habit is. Subsequent research has supported the idea that habit formation often takes weeks or months, not just days, and that complexity matters. For instance, a 2015 study found that when people tried to form an exercise habit, those who succeeded needed to repeat the exercise at least 4 times a week for 6 weeks before it became more automatic. More complex behaviors, especially those that require significant effort or logistical planning, tend to need longer to become ingrained.
Another recent 2021 study by economist Colin Camerer and colleagues used machine learning to analyze habit formation data. It showed that a handwashing habit (a very simple behavior) could form in a matter of weeks, whereas a gym habit might take around 6 months to become routine. Handwashing is quick, easy, and has frequent cues (like using the restroom), so it locks in faster. Exercise is more involved (change clothes, exert effort) and may happen only a few times a week, so it naturally takes longer to stick. The upshot of the research is: there’s a range, not a rule. Three weeks is usually far too short for most substantial habits, and even two months is just an average. Depending on what you’re trying to do, expect potentially a few months of consistent practice. But also know that if you miss a day or two, you haven’t reset the clock to zero. It’s a cumulative process.
Why Does Habit Formation Time Vary?
Several factors explain why one habit might lock in quickly and another slowly:
Complexity and Difficulty: Simple actions (drinking water, taking a daily vitamin) become habitual
faster because they require little effort and can be done every day with ease. Harder behaviors (like a workout routine or a strict diet change) demand more motivation and energy, so it takes longer for your brain to make them automatic. They also might not be done daily (maybe you exercise 3x a week), giving fewer repetitions to reinforce the habit.
Frequency of Repetition: The more often you repeat a behavior, the more chances your brain has to
associate it with the context and make it a habit. A daily habit will generally form faster than a weekly habit. If you want to build a habit, finding a way to do a small version of it daily can speed up the process. For example, doing 10 minutes of practice every day might build a habit faster than 1 hour of practice twice a week.
Consistency of Context: Habits form when behaviors happen consistently in the same context
(same time, place, or cue). If the context keeps changing, it’s harder for the cue to consistently trigger the routine. Doing something “at around 7am on weekdays in my kitchen” gives a stable context that your brain can latch onto. If you do it at different times and places each day, it may take longer to form the habit, because you’re essentially trying to form multiple habits (one for each context).
Reward Value: The more immediately rewarding a behavior is, the quicker your brain will want to
make it a habit. Unfortunately, this is why unhealthy habits (like eating cookies or checking social media) can form so easily – they give lots of quick pleasure. If a habit isn’t inherently fun (say, doing burpees), it helps to pair it with a reward or positive experience to help reinforce it. Over time, as you start feeling the intrinsic rewards (like feeling stronger or more energized from exercise), that helps too.
Individual differences: People vary in how quickly they form habits. Some have personalities or
genetics that incline them to routine and repetition, others crave variety. There’s even some evidence that individuals with better working memory and consistency in behavior might form habits a bit faster, but research is ongoing. The key is not to compare yourself too much with others – if your friend forms a habit in 4 weeks and you take, that’s okay. Focus on your own progress. Focus on the Process, Not a Magic Number Knowing that 21 days is a myth and 66 days is an average, what’s the practical takeaway?
Don’t get discouraged if three weeks pass and your habit isn’t automatic yet. It’s completely normal
for it to take longer. There’s nothing wrong with you or the habit – you probably just need more repetitions. As one article put it, “There is no need to judge yourself if you can't master a behavior in 21 short days. It's supposed to take longer than that!”. Understanding this prevents unnecessary disappointment. Instead of thinking, “Ugh, I’m past 21 days and this still feels like work, I must be failing,” you can think, “Okay, I’m only partway there, it’s getting easier than it was initially, and if I keep going it will likely get even easier in the next few weeks.”
Use the numbers as guidelines, not strict deadlines. It can be motivating to mark Day 21 or Day 66 on
your calendar as milestones, but remember they’re not magical transformation days. Some habits might click around that time, others will not. Instead of asking “How many days until this habit is formed?”, a better mindset might be, “Each day I do this, I’m strengthening the habit, no matter how small the increment.” Habits are a spectrum of automaticity, not an on/off switch. You may notice after a couple of weeks it’s becoming easier, after a month easier still, and maybe after three months you do it with hardly any thought. It’s gradual.
Embrace longer timelines as normal. Realizing that habit formation can take months can actually be
inspiring in a way. Big life changes aren’t quick fixes; they require sustained effort. By accepting that, you can mentally prepare for the journey. One psychologist noted, “habits are not a finish line to cross in days, 30 days, or whatever—it’s a lifestyle to be lived”. In other words, once you integrate the habit, you keep it as part of your life (“after” doesn’t really come, there is only “during,” as long as you want the habit). This perspective helps you commit for the long haul.
Concentrate on consistency and strategy. Instead of counting days, put your energy into structuring
your habit for success. Make a specific plan (what time, where, how you’ll do it). Use habit stacking (attach the new habit to an existing routine as a cue). Track your habit streaks to give yourself small wins. Set up rewards for sticking to it weekly. These tactics will carry you through the initial “hard” phase until the habit picks up its own momentum.
Be patient and forgiving with yourself. If you miss a day, don’t abandon the habit. As mentioned
earlier, missing one opportunity doesn’t materially affect long-term habit formation. The key is to get back on track the next day. Think progress, not perfection. Also, if you find yourself struggling after, say, 30 days, revisit your approach rather than blaming your willpower. Maybe the habit as defined was too ambitious (try scaling it back to something easier, then build up). Maybe your cue isn’t obvious enough (adjust it). Use each week as feedback to tweak the system.
The Verdict: How Long Should You Expect?
If pressed to give a number, telling people to expect around 2–3 months of daily repetition to form a moderate complexity habit is reasonable given the evidence. Simple habits might take a bit less, complex ones more. The range is big, but psychologically it helps to prepare for a few months – that way you won’t quit too early thinking it isn’t working. But more importantly, recognize that the exact number of days isn’t the end goal. Ultimately, a habit is formed when you feel that doing the behavior is almost automatic, and not doing it feels off. Whether that happens on day 45 or day 145 doesn’t matter as much as the fact that it will happen if you keep consistent and set yourself up well.
In summary: - The 21-day rule is a myth – an oversimplification from anecdotal origins. - Studies show habit formation often takes weeks to months, with 66 days being an average in one landmark study. Variation is normal: It depends on the person and the habit (anywhere from a few weeks to many months). - Instead of fixating on a number, focus on daily practice, good habit-building techniques, and patience. So, how long does it really take to form a habit? As long as it takes – and that’s okay. What matters is starting your habit journey and sticking with it. If you do that, the habit will eventually stick with you.