How Long Does It Take to Form a Habit? The 66-Day Study vs the 21-Day Myth

It takes about two months for a new daily habit to feel automatic, not 21 days. In the best-known study on the question, the median was 66 days, but individual times ranged from 18 to 254 days depending on the person and the habit (Lally et al., 2010). A 2024 review of later studies landed in the same place: medians of 59 to 66 days, with big differences between people.

What the 66-day study found

In 2010, Phillippa Lally and her team at University College London asked 96 volunteers to pick one new behavior and do it once a day in the same situation, for example "after breakfast", for 12 weeks. People chose things like drinking a bottle of water with lunch, eating a piece of fruit with lunch or going for a 15-minute run. Every day they rated how automatic the behavior felt.

82 people gave enough data. For most, automaticity rose quickly in the first weeks and then flattened out, like a curve reaching a ceiling. The researchers measured how long each person took to reach 95% of their own ceiling:

Two details matter more than the headline number. First, the 66 days is a median from the 39 people whose data fit the curve well, so it's a rough guide, not a law. Second, missing one day did not materially change the process. Doing the behavior consistently was what helped.

Where the 21-day myth comes from

The 21 days goes back to Maxwell Maltz, a plastic surgeon who wrote Psycho-Cybernetics in 1960. He noticed that his patients took about 21 days to get used to their new appearance. Self-help writers later turned that observation into a rule for habits, and it stuck.

It was never a study of habit formation. Researchers who later reviewed the evidence for GPs called it a myth and suggested telling patients to expect about ten weeks instead (Gardner et al., 2012). That matters in practice: if you expect a habit to be automatic in three weeks and it isn't, it's easy to decide you've failed and quit right when the curve is still climbing.

What newer research adds

• A 2024 review. Pooling 20 studies with 2,601 adults, a systematic review found that the four studies measuring time to habit reported medians of 59 to 66 days and means of 106 to 154 days, with individual times from 4 to 335 days. Morning habits and habits people chose themselves tended to be stronger (Singh et al., 2024).
• Gym vs handwashing. Using over 12 million gym check-ins and over 40 million hospital handwashing events, researchers found it typically takes months to form a gym habit but only weeks to form a handwashing habit at work (Buyalskaya et al., 2023).
• New gym members. In a 12-week study of new gym members, going about four times a week for at least six weeks was the minimum for an exercise habit to form (Kaushal and Rhodes, 2015).

The pattern across all of them: small, frequent actions tied to a stable cue form fastest. Big, effortful ones take longer.

How to create a habit that sticks

This is the short version of the advice Gardner and colleagues give patients, plus one technique with strong evidence behind it.

1. Pick one habit. Choose something you want, not something someone told you to do. Self-chosen habits were stronger in the 2024 review.
2. Make it small. "Read two pages", not "read more". You can grow it once it runs on its own.
3. Tie it to a cue you already have. Something that happens every day in the same place: pouring your first coffee, brushing your teeth, getting off the bus.
4. Write it as an if-then plan. "After I pour my coffee, I read two pages." Across 94 tests, people who made if-then plans reached their goals more often than people who only set the goal, with a medium-to-large effect (Gollwitzer and Sheeran, 200638002-1)).
5. Do it every time the cue happens. Consistency is what builds the automatic link, so keep the same action in the same place while it forms.
6. Tick it off. The handout Gardner's team designed is a simple 10-week tick sheet. A paper calendar, a note on the fridge or an app all work.
7. If you miss a day, do it the next day. One miss doesn't undo the work.

An example with made-up numbers: you start a 10-minute walk after lunch on 4 January. By late January it still takes effort. Around early March, the median point, you might notice you're putting your shoes on without thinking about it. If you don't, nothing is wrong; you may just be on the slower side of the range.

What to do if it still feels hard at day 66

Keep going. The 66 days is the middle of a range, so about half the people in the study needed longer. A few things usually help:

• Check the cue. If you do the habit at different times or places each day, it has nothing stable to attach to. Pick one.
• Shrink it. If you skip often, the habit is probably too big for now.
• Remove what competes with it. If you meant to read before bed but end up scrolling, the phone wins because that habit is older. Keep the phone out of reach or lock the apps you open on autopilot; there's more on that in how to stop phone addiction.

Make the habit the key to your phone

In LockTy you pick daily goals like reading minutes, steps, water or training. Until you hit them, the apps you choose stay locked, so the new habit comes first and the scroll comes after.

Get

Habits you already want to build

The same rules apply to most daily routines. If your habit is a supplement, a cue next to the kettle and a tick sheet do most of the work, as in how to remember to take creatine. If you're building several at once, start with the one that matters most and set it up as a daily goal: how to set daily goals walks through it.

The short version: plan for about two months, keep the cue the same, and don't treat a missed day as a reason to start over.