Habit Formation Calculator

This is not a prediction. It is the published range: in the studies that measured it, a new daily habit took a median of 59 to 66 days to feel automatic, and individual people took anywhere from 4 to 335. Pick the kind of habit and the time of day to see where the studies put the middle, and how far the tail runs.

Kind of habit

Time of day

Where the studies put it

Range of individual people Projected past the end of the study Median or reported time to plateau Mean The middle of the published data

The four studies behind the chart

Study	People	Study length	What it found
Lally and colleagues, 2010 One eating, drinking or activity behaviour, tied to a daily cue	96 volunteers	84 days	Time to plateau 66 days on average; individual fits from 18 to 254 days. Exercise took about 1.5 times as long as eating or drinking. About half were not at a habit-level score by day 84.
Keller and colleagues, 2021 One everyday eating behaviour, tied to a routine or to a clock time	192 adults	84 days	A median of 59 days to peak automaticity among the people who formed a habit. Routine cues and time cues worked equally well.
Singh and colleagues, 2024 A systematic review and meta-analysis of 20 studies	2,601 people	20 studies	Medians of 59 to 66 days, means of 106 to 154, individual times from 4 to 335. Morning and self-chosen habits tended to be stronger; no significant difference between exercising, drinking water and eating fruit.
Fournier and colleagues, 2017 One daily stretch, after waking or before bed	48 students	90 days	Extrapolated automaticity at about 106 days for the morning group and 154 for the evening group. One small study; both figures are projections.

The bars above are these rows on a day axis. Nothing is added to them except the highlight, and the exercise band is our own arithmetic, named as such in the method note below.

The shape of the curve, and your own

Every study fitted the same shape to each person: a fast climb, then a slowing, then a plateau. This one is scaled so it reaches 95 per cent at the highlighted day. Rate the four statements below once a week and your scores are drawn over it.

Typical shape Your weekly checks

Weekly self-check

The four statements of the SRBAI, the questionnaire the studies used. Think of the one habit you are building and rate each statement from 1, strongly disagree, to 7, strongly agree.

Doing this habit is something…

I do automatically.

I do without having to consciously remember.

I do without thinking.

I start doing before I realise I am doing it.

1 · strongly disagree 7 · strongly agree

Saved in this browser. A score of 4 is no automaticity at all; 28 is the ceiling.

How the ranges are drawn

No figure on this page comes from anything you type. Every bar is a published figure placed on a day axis that runs from 0 to 340. Lally and colleagues (2010): 96 volunteers, 84 days, an eating, drinking or activity behaviour tied to a daily cue; time to plateau 66 days on average, individual fits from 18 to 254 days. The study ran for 84 days, so every figure past that is where a person's curve was heading rather than a day anyone reached, and the bar is drawn fainter from day 84 on. Keller and colleagues (2021): 192 adults, 84 days, an everyday eating behaviour; a median of 59 days among the people who formed a habit; no range was reported, so the page draws a mark and no bar. Singh and colleagues (2024): a review of 20 studies and 2,601 people; medians of 59 to 66 days, means of 106 to 154, individual times from 4 to 335. Fournier and colleagues (2017): 48 students, 90 days, one daily stretch; extrapolated automaticity at 106 days for the morning group and 154 for the evening group.

The habit-type switch does two things. For eating, drinking and other habits it highlights the two medians, 59 and 66. For exercise it multiplies both by 1.5 and highlights about 89 to 99 days. That multiplier is our own arithmetic on one sentence in the British Psychological Society's summary of Lally's study — exercise took about one and a half times as long as eating or drinking — applied to pooled medians that already include the exercise participants, so it overstates a little, and the 2024 review found no significant difference between exercising, drinking water and eating fruit. It is drawn as a rough band and named as ours. The time-of-day switch moves nothing: it lights the Fournier mark for the time you chose, because one study of 48 people is a reason to look, not a number to plan by.

The curve underneath is the shape those studies fitted: an asymptote scaled so it reaches 95 per cent at the highlighted day, which is the plateau definition Lally used. It is the typical shape and not anyone's data. The weekly self-check asks the four statements of the Self-Report Behavioural Automaticity Index, each rated 1 to 7, and plots the total from 4 to 28 on the same axis. Your points are saved in this browser and drawn over the curve; they are your own ratings, not a measurement of anything else.

Where these numbers come from

1. How are habits formed: Modelling habit formation in the real world — Lally P, van Jaarsveld CHM, Potts HWW, Wardle J, European Journal of Social Psychology 40(6):998–1009, 2010
2. How to form a habit — British Psychological Society, Research Digest (summary of Lally et al. 2010)
3. Making health habitual: the psychology of 'habit-formation' and general practice — Gardner B, Lally P, Wardle J, British Journal of General Practice 62(605):664–666, 2012 (PMC)
4. Habit formation following routine-based versus time-based cue planning: A randomized controlled trial — Keller J, Kwasnicka D, Klaiber P, Sichert L, Lally P, Fleig L, British Journal of Health Psychology, 2021 (PubMed)
5. Time to Form a Habit: A Systematic Review and Meta-Analysis of Health Behaviour Habit Formation and Its Determinants — Singh B et al., Healthcare (Basel) 12(23):2488, 2024 (PMC)
6. Effects of circadian cortisol on the development of a health habit — Fournier M, d'Arripe-Longueville F, Rovere C, Easthope CS, Schwabe L, El Methni J, Radel R, Health Psychology, 2017 (PubMed)
7. Towards parsimony in habit measurement: testing the convergent and predictive validity of an automaticity subscale of the Self-Report Habit Index — Gardner B, Abraham C, Lally P, de Bruijn GJ, International Journal of Behavioral Nutrition and Physical Activity 9:102, 2012 (PMC)

Nothing on this site is medically reviewed. Every figure above was read out of the code that runs on this page, and where a number is our own judgement rather than a published one, the note says so and cites nothing. Method last checked 25 September 2026.

Why the answer is a range and not a date

Every study of habit formation reports the same shape: a group of volunteers, a daily behaviour tied to a cue, a questionnaire each day asking how automatic it felt, and a curve fitted to each person. The curves climb fast, slow down, and level off. The day they level off is the number that gets quoted. It is different for every person in every study, and the spread is the finding.

In the 2010 study by Lally and colleagues, the time to plateau was 66 days on average, and individual fits ran from 18 to 254 days. About half the volunteers had not reached a habit-level score when the 84-day study ended. A 2021 trial of 192 adults found a median of 59 days. A 2024 review of 20 studies and 2,601 people found medians of 59 to 66 days, means of 106 to 154, and individual times from 4 to 335. The means sit far above the medians because a minority of people take a very long time.

A single date would hide all of that. If you expect the habit to run on its own by day 66 and it does not, you are not behind; you are in the half of the room the median never described. Two things did move the numbers in the studies: simpler behaviours plateaued sooner than elaborate ones, and morning habits tended to be stronger. Neither turns a range into a date.

What you can measure is your own curve. The studies used four questions, rated once a day; once a week is enough to see the shape. Do the behaviour, tie it to the same cue, and ask the questions. If the score is still climbing, the habit is still forming.

Frequently Asked Questions

Can a calculator tell me when my habit will be automatic?

No, and this one does not try. The studies report medians and ranges for groups of volunteers, and the spread inside every group is wide: 18 to 254 days in the best-known study, 4 to 335 across a 2024 review. The tool draws those ranges and marks the middle. Where you land inside them depends on you, the habit and the days you actually do it.

What does the habit formation curve look like?

A steep climb that flattens. In the studies, the sense that a behaviour runs on its own rose fast in the first weeks, then each repetition added a little less, until the curve levelled off. Researchers fitted that shape to each person's daily ratings and read off the day it reached 95 per cent of its ceiling. Most of the gain comes early; the last stretch is slow.

Is 66 days the number of days it takes to form a habit?

It is the time to plateau reported in one study of 96 people, and only that. Individual times in the same study ran from 18 to 254 days. A 2021 trial of 192 adults found a median of 59 days, and a 2024 review of 20 studies found medians of 59 to 66 with means of 106 to 154, because a minority of people take a very long time.

Why does an exercise habit take longer to form?

In the 2010 study, people who chose an exercise behaviour took about one and a half times as long to reach their plateau as people who chose an eating or drinking behaviour, and the authors put it down to complexity: fifty sit-ups are more to arrange than a glass of water. A 2024 review of 20 studies did not find a significant difference between exercising, drinking water and eating fruit, so treat the multiplier as one study's finding.

Does the time of day change how fast a habit forms?

One small trial says it might. Forty-eight students did a daily stretch for 90 days, half after waking and half before bed. Extrapolating the curves, the morning group reached automaticity at about 106 days and the evening group at about 154. A 2024 review also found morning habits tended to be stronger. That is one study of 48 people and one review: a reason to prefer the morning, not a rule.

What is the SRBAI self-check?

The Self-Report Behavioural Automaticity Index: four statements about one behaviour, each rated from 1 to 7, so the score runs from 4 to 28. It is the questionnaire several of these studies used to measure how automatic a habit felt. The optional weekly check on this page asks the same four questions and plots your scores against the typical curve. Your scores are saved in this browser.

Count the days you did it in Aura

Aura checks a habit off in one tap and keeps a grid of the days you kept it, so at week eight you can look at the record instead of guessing.