How long does it take to form a habit?

The 66 days come from one study by Phillippa Lally and colleagues at University College London. They asked 96 volunteers to each pick one new eating, drinking or exercise habit, such as a glass of water after breakfast. Each person did it daily, after the same cue (a fixed moment in their day that prompts it, like finishing breakfast), for 12 weeks (Lally and colleagues, 2010).

Every day, each person rated how automatic the behavior felt, meaning how far they did it without having to think or decide. Plotted over time, the ratings rose quickly at first, then slowed, then leveled off. The researchers counted a habit as formed once the ratings reached 95% of the level where they flattened out. Not everyone’s ratings followed such a clear curve, but for the people whose did, the median (the middle person, with everyone lined up from quick to slow) was 66 days.

The study watched people for 84 days. So the slow end of the range, 254 days, is where one person’s curve was heading if it kept going, worked out from its shape rather than a day anyone observed. That detail is missing from most pages that quote the number.

Two other findings from the study matter as much as the average. Missing one day did not really change how the habit formed. And simple actions got there sooner than longer routines: a glass of water became automatic faster than 50 sit-ups (Gardner, Lally and Wardle, 2012).

A systematic review is a study of studies: researchers gather every study on one question and compare the results. A 2024 review by Singh and colleagues pulled together 20 studies of 2,601 people forming health habits (Singh and colleagues, 2024). Four of them timed how long a habit took. The medians ran from 59 to 66 days. The means, the ordinary averages, ran from 106 to 154 days, and individual people took anywhere from 4 to 335 days.

The means came out well above the medians, and that gap tells you something. Most people land around two months, but a long tail of slow habits pulls the average up. The review’s own summary is that health habits usually take 2 to 5 months.

One of those studies, a trial by Keller and colleagues that followed 192 adults for 84 days, found a median of 59 days for those who formed the habit (Keller and colleagues, 2021). Only 23% of the people in it reached the score the researchers set for a formed habit before the study ended. Starting is common; finishing inside 12 weeks is not.

The 21-day rule comes from Maxwell Maltz, a plastic surgeon, in his 1960 book Psycho-Cybernetics. He wrote that it “usually requires a minimum of about 21 days to effect any perceptible change in a mental image” (Maltz, 1960).

He was describing patients getting used to a new face, not people forming habits. And he said a minimum, which the retelling turned into a deadline. A paper for family doctors traced the myth to those surgery patients and suggested telling people to expect about 10 weeks instead (Gardner, Lally and Wardle, 2012).

The three-week rule does real harm in one way. People who still find the habit hard after three weeks decide they have failed, at the point where the curve is often still climbing.

The range is wide because the time depends on the behavior, the cue and the person. The studies point to a few things that move it.

• How simple the action is. A glass of water became automatic sooner than a set of sit-ups (Gardner, Lally and Wardle, 2012).
• How steady the cue is. The habit forms on a cue you meet every day, such as “after dinner”. In one trial, a routine cue and a clock time worked about as well as each other (Keller and colleagues, 2021).
• How often you repeat it. In the Lally study, people who did the behavior more consistently tended to show a clearer curve (Lally and colleagues, 2010).
• Whether you chose it. Habits people picked for themselves grew stronger than assigned ones, in the studies the review pooled (Singh and colleagues, 2024).
• The time of day, maybe. In one study, morning stretching became automatic sooner than evening stretching: a mean of 106 days against 154 (Fournier and colleagues, 2017). That is a single study of one behavior.

The advice that comes out of this research is short, and it is the advice the researchers themselves give (Gardner, Lally and Wardle, 2012).

1. Pick one small action you want to do every day, and choose it yourself.
2. Tie it to a cue you meet daily, in the same place: after dinner, after you pour the first coffee.
3. Do it every time you meet the cue. Keep the cue the same, even when the action feels easy.
4. If you miss a day, do it the next day. One miss did not undo the curve in the study.
5. Expect weeks, not days. Plan for ten weeks, and check how automatic it feels once a week.

If the habit you want is really about stopping something, read how long it takes to break a habit. Breaking follows different rules.

The steps above line up with the four laws in James Clear’s Atomic Habits, a popular book from 2018 that splits a habit into a cue, a craving, a response and a reward (Clear, 2018). Here are his laws for building a habit, in our words, with the research behind each.

• Make it obvious. Tie the habit to one cue you meet every day. Plans that name the moment in advance (“after dinner, I will read”) helped people reach their goals across 94 tests (Gollwitzer and Sheeran, 2006).
• Make it attractive. Pick a version you enjoy. In one study, people who found the behavior pleasant gained more habit strength from each repeat (Judah and colleagues, 2018).
• Make it easy. Start small, since a glass of water became automatic sooner than 50 sit-ups (Gardner, Lally and Wardle, 2012).
• Make it satisfying. Let something good come straight after while the habit is new, because habits grow as people repeat what gets them something they want (Wood and Rünger, 2016).

The book is not a study, and the research puts most of the weight on the cue and the repeats. The whole loop, each law set against its research, and a map for your own habit are on habit formation and the habit loop.

Plan for about ten weeks, not three. Pick one small action, tie it to a cue you meet every day, and do not panic over a missed day. Check once a week whether it feels more automatic.

Day one can be tonight. Pick the cue and start counting.

1. Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W. and Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998 to 1009.
2. Singh, B., Murphy, A., Maher, C. and Smith, A. E. (2024). Time to Form a Habit: A Systematic Review and Meta-Analysis of Health Behaviour Habit Formation and Its Determinants. Healthcare, 12(23), 2488.
3. Keller, J., Kwasnicka, D., Klaiber, P., Sichert, L., Lally, P. and Fleig, L. (2021). Habit formation following routine-based versus time-based cue planning: A randomized controlled trial. British Journal of Health Psychology, 26(3), 807 to 824.
4. Fournier, M., d'Arripe-Longueville, F., Rovere, C., Easthope, C. S., Schwabe, L., El Methni, J. and Radel, R. (2017). Effects of circadian cortisol on the development of a health habit. Health Psychology, 36(11), 1059 to 1064.
5. Gardner, B., Lally, P. and Wardle, J. (2012). Making health habitual: the psychology of 'habit-formation' and general practice. British Journal of General Practice, 62(605), 664 to 666.
6. Gardner, B., Abraham, C., Lally, P. and de Bruijn, G.-J. (2012). Towards parsimony in habit measurement: Testing the convergent and predictive validity of an automaticity subscale of the Self-Report Habit Index. International Journal of Behavioral Nutrition and Physical Activity, 9, 102.
7. Verplanken, B. and Orbell, S. (2003). Reflections on past behavior: A self-report index of habit strength. Journal of Applied Social Psychology, 33(6), 1313 to 1330.
8. Maltz, M. (1960). Psycho-Cybernetics. Prentice-Hall; quoted from the publisher's preview of the current Profile Books edition.
9. Clear, J. (2018). Atomic Habits: An Easy and Proven Way to Build Good Habits and Break Bad Ones (the author's summary of its framework). Avery; the four laws as the author lists them on jamesclear.com.
10. Gollwitzer, P. M. and Sheeran, P. (2006). Implementation intentions and goal achievement: A meta-analysis of effects and processes. Advances in Experimental Social Psychology, 38, 69 to 119.
11. Judah, G., Gardner, B., Kenward, M. G., DeStavola, B. and Aunger, R. (2018). Exploratory study of the impact of perceived reward on habit formation. BMC Psychology, 6, 62.
12. Wood, W. and Rünger, D. (2016). Psychology of Habit. Annual Review of Psychology, 67, 289 to 314.