How long does it really take to build a habit?

Short answer: about two months on average — but anywhere from a couple of weeks to most of a year. In the best-known study, the median time for a new daily habit to feel automatic was 66 days, with individuals ranging from 18 to 254 days (Lally et al., 2010). Simple habits tend to form faster than demanding ones, and missing the odd day doesn’t reset the clock.

You’ve probably heard that it takes 21 days. It’s a tidy number, and it has been repeated so often that it feels like science.

It isn’t. The 21-day figure traces back to Maxwell Maltz’s 1960 self-help book Psycho-Cybernetics, and it described how long his patients seemed to take to adjust to a change — “a minimum of about 21 days” — not how long a new behaviour takes to become automatic.

What does the research actually say?

The study most people cite is Lally and colleagues, 2010, published in the European Journal of Social Psychology. Ninety-six volunteers each picked one new daily behaviour — eating a piece of fruit with lunch, drinking a bottle of water, running before dinner — and reported every day for twelve weeks how automatic it felt.

Eighty-two gave enough data to analyse. For the 39 whose progress fitted the researchers’ model well, the median time to reach 95% of their plateau of automaticity was 66 days. But the range was enormous: from 18 days to 254 days. To see where 18, 66 and 254 days fall for a habit you’ve already started, put your start date into the habit formation calculator.

Does it depend on the habit?

Yes — and on the person. In Lally’s study, the exercise group took about one and a half times longer than the eating and drinking groups (a median of 91 days, against 59 and 65), though the authors note the study wasn’t large enough to treat that difference as definitive.

Later research points the same way:

• Gym vs handwashing. A 2023 machine-learning study of more than 30,000 gym-goers and 3,000 hospital workers found that gym attendance took months to become habitual, while hospital handwashing took weeks. After a published correction, the gym estimate is about 68 to 78 days — roughly two to three months; handwashing typically settled after 9 to 10 shifts, about a couple of weeks.
• A review of the evidence. A 2024 systematic review of 20 studies and 2,601 participants found that median times ranged from 59 to 66 days and mean times from 106 to 154 days, with individuals ranging from 4 to 335 days. Its conclusion: habits can start forming within about two months, but the time varies a lot from person to person.
• How often matters. A study of 111 new gym members found that exercising at least four times a week for six weeks was the minimum needed to establish an exercise habit.

What does the range mean for you?

• There’s no finish line on day 21. If a habit still takes effort in week four, nothing has gone wrong. You’re simply in the middle.
• Automaticity rises quickly, then flattens. Early repetitions make the biggest difference. That’s why the first few weeks feel like the hardest work — they’re the part doing the most.
• A missed day isn’t a reset. In Lally’s study, missing one opportunity didn’t materially affect the process. Consistency over weeks mattered; perfection didn’t.

How to use this

Expect two to three months, not three weeks

Plan for the real timeline. If you go in expecting 21 days, week five feels like failure. If you go in expecting a couple of months, week five is just week five.

Make it smaller than you think

Simple behaviours tend to become automatic faster, so start with a version that’s almost trivial — two pages, not a chapter. You can raise it once it runs on its own.

Tie it to something you already do

The volunteers in Lally’s study attached their new behaviour to a moment in their day — with lunch, before dinner. Repeating an action in the same context is what lets the context start to trigger it. There’s a whole post on habit stacking and choosing a good cue.

Do it often

If a habit only happens once a week, it has fewer chances to become automatic. Where you can, choose a daily or near-daily version.

If you’d rather see the weeks add up on paper, print a free monthly habit tracker and keep it somewhere you’ll pass every day.

The short version

• 21 days is a myth from a 1960 self-help book. The best-known study found a median of 66 days, ranging from 18 to 254.
• Newer research agrees: typically around two months, with big differences between people and habits.
• Simpler, more frequent habits tend to form faster, so start small and do it often.
• Missing a day now and then doesn’t reset the clock. Judge progress by how automatic it feels, not by the date.