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

Every January, millions of people decide to exercise more, read more or eat better. By February, most of those plans have faded. It’s easy to blame willpower. But research on habits suggests the problem is usually something else: we expect habits to form faster than they do, and we rely on motivation for a job that motivation isn’t built to do.

Where “21 days” came from

The claim that it takes 21 days to form a habit is everywhere, but it doesn’t come from a study of habits. It is usually traced to Psycho-Cybernetics, a 1960 self-help book by Maxwell Maltz, a plastic surgeon. He observed that patients took “a minimum of about 21 days” to get used to changes such as a new face. Over the years, “a minimum of about” was dropped, and the number became a rule.

What the research actually found

In 2009, a team led by the psychologist Phillippa Lally at University College London ran one of the first studies to measure habit formation directly. Ninety-six volunteers each chose a new daily behaviour, such as eating a piece of fruit with lunch, drinking a bottle of water or going for a run before dinner, and did it in the same situation each day. Every day, they rated how automatic the behaviour felt.

The results, published in 2010, showed:

• Habits form gradually. Automaticity rose quickly at first, then levelled off, like a curve flattening out.
• It took a median of 66 days for people to reach close to their highest level of automaticity.
• The range was huge: from 18 days to an estimated 254 days, depending on the person and the behaviour. Simple habits, like drinking water, formed faster than harder ones, like exercise.
• Missing one day didn’t really matter. An occasional missed day had no meaningful effect on the overall progress.

Consistency over weeks matters more than a perfect streak.

What a habit actually is

Psychologists define a habit as an action that is triggered automatically by a cue, because you have done it many times in that same situation. The cue can be a place, a time of day, a person, a feeling or the action you just finished.

Brushing your teeth is a good example. You don’t decide to do it each night. Walking into the bathroom before bed triggers it. Research by the psychologist Wendy Wood and colleagues, in which people kept diaries of what they were doing and thinking, found that around 43% of everyday actions were done almost automatically, often while thinking about something else.

That is why habits are so powerful. Once formed, they don’t need motivation or willpower. They just need the cue.

How to make a new habit stick

1. Pick a clear cue

Vague goals, like “exercise more”, don’t give your brain a cue to link to. Specific plans do. Psychologists call these implementation intentions: plans in the form “When X happens, I will do Y.” For example: “When I finish my morning coffee, I will walk for ten minutes.” A review of 94 studies by Peter Gollwitzer and Paschal Sheeran found that plans like this made people noticeably more likely to reach their goals.

2. Attach it to something you already do

Your existing routines are full of reliable cues. Linking a new habit to one of them, sometimes called “habit stacking”, gives it a ready-made trigger: stretching after you brush your teeth, or reading a page after you get into bed.

3. Make it small and easy to start

A habit forms through repetition, so the most important thing early on is doing it often. Start smaller than you think you need to. Two push-ups done every day build a stronger habit than fifty done once. You can increase the amount once the action feels automatic.

4. Keep the situation the same

Doing the action at the same time and in the same place helps the link form. Changing the situation every day means the cue keeps changing.

5. Reduce friction

Make the good habit easier and the bad one harder. Put your running shoes by the door. Keep fruit on the counter and biscuits in a high cupboard. Wood’s research suggests small changes in effort, such as a few extra steps, can have a surprisingly large effect on what we do.

6. Don’t panic after a missed day

If you miss a day, just carry on the next day. The research suggests one slip doesn’t undo your progress. Missing many days in a row is what weakens the link.

Breaking a bad habit

Bad habits follow the same rules, which is why they are hard to break with willpower alone. The cue still fires the action. Two approaches tend to help:

• Change or avoid the cue. If you always check your phone in bed, charge it in another room.
• Replace rather than remove. Keep the cue but swap the action, for example reaching for water instead of a sugary drink when you sit down to work.

Life changes, such as moving house or starting a new job, are a good time to do this, because many old cues disappear at once.