How Long Does It Take to Form a Habit? What the Research Actually Says

Where the 21-day idea came from

In 1960, a plastic surgeon named Maxwell Maltz published Psycho-Cybernetics, a self-help book about self-image. In its preface he wrote that it usually takes a minimum of about 21 days to see a change in a person's mental image, with examples such as patients getting used to a new face after surgery.

That is an observation about getting used to a change, and Maltz said "a minimum". Over the following decades it was simplified into "21 days to form a habit", a phrase with no study behind it. Researchers at University College London have traced the figure back to Maltz and called it unfounded as a basis for habit formation.

The study behind 66 days

The research most often quoted on this question comes from Phillippa Lally and colleagues at University College London, published in the European Journal of Social Psychology.

They asked 96 volunteers to pick one eating, drinking or exercise behaviour and do it once a day in the same context, for example "after breakfast", for 12 weeks. Choices included eating a piece of fruit with lunch, a 15-minute run before dinner and 50 sit-ups after morning coffee. Every day, participants recorded whether they had done it and rated how automatic it felt, using statements such as "I do it without thinking".

Automaticity rose quickly at first and then levelled off, like most learning curves. For the people whose data fitted that curve well, the median time to reach 95% of their personal plateau was 66 days. The spread was the more interesting result: from 18 days for the fastest to a projected 254 days for the slowest, well beyond the 12 weeks of the study.

Two details matter for anyone starting a habit. Simple behaviours became automatic faster than demanding ones: drinking a glass of water levelled off sooner than 50 sit-ups. And missing a single day did not materially affect the process. People who performed their behaviour more consistently showed a clearer habit curve.

What bigger studies found since

Gym visits take months, handwashing takes weeks

In 2023, researchers from Caltech, the University of Chicago and the University of Pennsylvania applied machine learning to two very large data sets: more than 12 million gym check-ins from over 30,000 members of a US gym chain, and more than 40 million handwashing records from over 3,000 hospital workers. They treated a habit as formed once someone's behaviour became highly predictable from its context.

Their headline finding, published in PNAS: going to the gym typically took months to become a habit, about six months on average according to Caltech's summary, while handwashing in the hospital became habitual within weeks. For most gym-goers, the time since their last visit mattered most, and a longer gap made the next visit less likely. Most were also more likely to go on the same days of the week. The time of day made no difference.

A 2024 review: about two months is typical, the range is huge

A systematic review from the University of South Australia, published in Healthcare in 2024, pooled 20 studies with 2,601 participants. Four of them reported how long habits took to form: median times of 59 to 66 days, mean times of 106 to 154 days, and individual results anywhere from 4 to 335 days. The gap between median and mean tells you something on its own: a few slow cases pull the average up, while most people land closer to two months.

The habits that grew strongest were those done often, those people chose for themselves and, in general, those done in the morning.

Why some habits take longer than others

• Complexity. A glass of water after breakfast is one step. A run is a dozen small decisions about clothes, route, weather and energy. The more steps, the longer the road.
• Frequency. Daily repetition gives more practice than three times a week. Weekly habits can still form; they simply get fewer chances to.
• A stable cue. Habits attach to context: a place, a time, the thing you did just before. "Whenever I get a moment" gives a habit nothing to attach to.
• Choice. Habits people picked for themselves tended to grow stronger than ones that were assigned to them.
• Gaps. One missed day is noise. In the gym data, the length of the gap since the last visit was the biggest warning sign.

How to use this when you start a habit

Five steps, drawn from the studies above and from the advice UCL's researchers give patients.

Tracking a habit in RytePad

RytePad is not a dedicated habit tracker: there are no repeating tasks yet and no habit charts. It does have three things that help a new routine stay visible:

• A day streak in Daily Tasks. The progress line above your list counts the days in a row on which you completed at least one task. Add the habit as a task on the days you plan to do it, and it becomes part of a chain you can see. Free on every plan.
• A writing streak in the Diary. If your habit is journaling, the diary counts the days in a row with an entry and shows your recent days as dots.
• Monthly goals. On Pro, set a goal for the month, such as "Walk 20 minutes on 20 days in November", in the goal tracker. The month picker shows an orange dot while a month still has goals to do and a blue one once they are all achieved.

Four mistakes that stall a new habit

Habit formation: your questions answered