How Long Does It Take to Form a Habit? 66 Days, Give or Take Months

The short answer

About two months for a simple daily habit, and often a lot longer. In the best-known study, the median was 66 days, and individual people ranged from 18 to 254 days. A 2024 review of the research found medians of 59 to 66 days, with individual estimates from 4 to 335 days.

So if you’re three weeks in and it still takes effort, nothing is wrong with you. That’s normal.

What the studies found

Lally and colleagues (University College London, European Journal of Social Psychology, 2010). 96 people each picked one eating, drinking or exercise behavior and did it once a day in the same situation, like “drink a glass of water after breakfast”, for 12 weeks. Every day they rated how automatic it felt. For a typical person, automaticity rose quickly at first and then levelled off. The median time to reach that plateau was 66 days, from 18 days for the fastest to an estimated 254 days for the slowest. Two other findings matter as much as the number:

Missing one day didn’t derail the process. One miss is not a reset to zero.
Exercise took longer. The median was 91 days for exercise habits, against 59 for drinking and 65 for eating ones, though the groups were too small to call that difference certain.

Singh and colleagues (Healthcare, 2024) pulled together 20 studies with 2,601 adults on health habits like exercise, healthy eating, flossing and taking vitamins. Only four studies measured the time directly, and they put the median at 59 to 66 days (means 106 to 154 days), with individual estimates from 4 to 335 days. Doing the habit more often, doing it in the morning, planning it, and finding it enjoyable or rewarding all helped it stick.

Where “21 days” came from

From a 1960 self-help book, Psycho-Cybernetics, by the plastic surgeon Maxwell Maltz. He wrote that it takes “a minimum of about 21 days” for people to adjust to a change, such as a new face after surgery. Over the years “a minimum of about 21 days” became “21 days”, and the self-help world kept it because it sounds doable. It was never a measurement of habit formation.

What to do with this

Plan for two months, not three weeks. Put a date eight to ten weeks out in your calendar and call that the finish line for “this should feel easier by now”.
Same trigger, every day. Tie the habit to something that already happens: after coffee, after brushing your teeth, when you sit down at your desk. Lally’s participants did their habit in the same situation every day.
Make it small enough to do on a bad day. Two pages, not a chapter. You can grow it once it’s automatic.
Don’t treat a miss as a fail. Get back on the next day. Lally’s data says one miss barely matters; giving up after one does.
Give the early weeks a payoff. Before a habit runs on its own, every repetition costs effort and pays back later. A small reward right after it, or a bigger one you’re working toward, gives you a reason to show up in the meantime. The 2024 review found that habits people find enjoyable or rewarding are more likely to stick. We know of no study showing a reward makes a habit form faster; its job is to keep you repeating until it does.

A tracker for the two months

Habit Rewards is a habit tracker built for that in-between stretch. Each habit you check off pays coins (1, 4, 8 or 16 by difficulty, or any number you set), and you spend them on rewards you price yourself: a coffee out, a new book, a movie night. It keeps your streaks, and a skip day for 10 coins keeps one bad day from breaking the chain.

Claiming a reward in Habit Rewards: Movie night for 25 coins

It’s free for up to three habits on iPhone and Android. For the paper route, the printable habit tracker lets you set a goal and a reward for each habit, and 70 ways to reward yourself has ideas for what to work toward.

FAQ

Is it 21 days or 66 days? 66 days is the median from an actual study; 21 days comes from a 1960 book about adjusting to change. For most people and most habits, plan on two months or more.

Why do some habits take so much longer? Some behaviors take longer (exercise habits took a median of 91 days in Lally’s study, against 59 for drinking water or similar), and some people simply take longer than others: the spread went from 18 to an estimated 254 days.

Does missing a day reset the clock? No. In Lally’s study, missing a single day didn’t materially affect how automatic the habit became. What hurts is stopping after the miss.

How do I know it’s a habit? When you start doing it without deciding to, and skipping it feels odd. That’s the “automaticity” the studies measure.

Sources

Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W., & Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998–1009.
Singh, B., et al. (2024). Time to form a habit: a systematic review and meta-analysis of health behaviour habit formation and its determinants. Healthcare.
Maltz, M. (1960). Psycho-Cybernetics. Prentice-Hall.

中文版：习惯养成要多久？ · 習慣養成要多久？

✅ Try Habit Rewards: the habit tracker that pays you

Every habit pays coins by how hard it is (1, 4, 8 or 16). Write your own reward list, put a coin price on each treat, and claim it once you've earned it.