How Long Does a Habit Really Take?

Where the 21 days came from, what the research actually found, why missing a day won’t cost you the habit, how to make a new habit easier to form, how to break an old one, and why enjoying it now matters more than the payoff later

Written by Ivana, psychologist and psychotherapist

14 minute read  ·  3,118 words

It’s day twenty-two. You’ve gone for a walk every morning for three weeks, more or less, and you were told that by now it would happen on its own. It doesn’t. This morning you stood by the door, looked at your shoes, and had the same small argument with yourself that you had on day one.

It’s easy to read that moment as a sign that something’s wrong with you, or with your willpower. It’s much more likely that the number was wrong.

The idea that it takes 21 days to form a habit is one of the most repeated “facts” in self-help. It just isn’t what the research found. The real answer is longer, it varies a lot from person to person, and in a way it’s much kinder to you.

The number started with a surgeon

In 1960 a plastic surgeon called Maxwell Maltz published a book called Psycho-Cybernetics (such a cool name tbh). He’d noticed that his patients seemed to take about three weeks to get used to their new face, and that people who had lost an arm or a leg often went on feeling it was there for about as long. The same thing seemed to happen when people moved. From observations like these, he wrote that it usually takes a minimum of about 21 days for an old mental image to fade and a new one to settle in.

So his number came from watching people get used to changes that had already happened to them. He did suggest practicing his exercises for 21 days, but as the least it might take to notice a change, not as the day a habit is finished. And he said a minimum.

A minimum became a promise

As the book was quoted and requoted, “a minimum of about 21 days” got shortened to “21 days”. It spread through self-help books, courses and apps, partly because it’s such a tidy number: long enough to sound like effort, short enough to feel doable. It was repeated so often that it started to sound like something someone had measured. For decades, almost nobody had.

What a habit actually is

In psychology, a habit isn’t just something you do often. It’s something you do automatically, set off by the situation you’re in, without having to decide. You sit down on the bus and your hand is already reaching for your phone. You walk into the kitchen and the kettle’s on before you’ve thought about it. Researchers call this quality automaticity.

A lot of everyday life runs this way. When students kept diaries of what they were doing through the day, somewhere between a third and a half of what they did was done almost every day, usually in the same place. Habits are also closely tied to the brain’s reward and learning systems, which is part of why the ones we’d rather break can be so stubborn.

So the useful question isn’t how many days you have to keep going. It’s how long it takes before doing it stops needing a decision.

Sixty-six days, not twenty-one

In 2010 Phillippa Lally and her colleagues in London published one of the first studies to actually measure this. They asked 96 volunteers to pick one new behavior, like eating a piece of fruit with lunch or going for a run before dinner, and to do it every day in the same situation. For twelve weeks, everyone logged whether they’d done it and how automatic it felt.

For the people whose results showed a clear curve, it took a medianmedianThe middle value: half the people took less time than this and half took more. Unlike an average, it isn’t pulled upward by the few who took a very long time. of 66 days for the new behavior to feel as automatic as it was going to get. That’s a little over two months, about three times longer than the famous 21 days.

The range is the real finding

That middle number hides how differently people got there. Some people got there in 18 days. Others would have needed about 254 days, which is more than eight months. A recent review found only a handful of studies that actually timed this, and together they point the same way: usually somewhere between two and five months, with individuals anywhere from 4 days to almost a year.

So if you’re at week three and it still feels like work, you’re not behind. You’re completely normal!

Some habits are quicker than others

It also depends on what you’re building. In Lally’s study, exercise habits seemed to take longer to settle than eating or drinking ones, although the study was too small to be sure. A much bigger study, which tracked tens of thousands of gym-goers and hospital workers, found a clear difference: hospital staff built a handwashing habit within a couple of weeks, while a gym habit usually took two to three months.

That makes sense when you think about it. Washing your hands is quick, and the cue is right in front of you. Getting to the gym means leaving the house, changing, and finding the time, and every one of those steps is a chance to decide not to.

Habits grow along a curve

In Lally’s study, automaticity didn’t switch on on a particular day. It rose quickly at first, when every repetition made a noticeable difference, and then more and more slowly, until it leveled off. The early weeks are when the most change happens, even though they’re also when the new behavior still feels the hardest. Move through the days below to see it.

Missing a day doesn’t reset the clock

Here’s one of the most useful findings, and one of the least known. In Lally’s study, missing a single day didn’t make a real difference to how the habit developed. What mattered was coming back to it over the weeks, not keeping an unbroken streak.

That matters, because so many of us give up the first time we miss a day, as if the streak was the thing we were building. The research suggests it never was. You can see it in the chart above: check “Miss a day on day 30” and watch how little changes.

Longer gaps are a different story. In another study, people who missed a whole week were more likely to drop the new behavior altogether. And when researchers tested 54 different ways of keeping gym members going, the one that worked best rewarded people for coming back after a missed workout. The slip was never the problem. Staying away is.

Why one slip can feel like the end

One missed day can make you want to give up entirely. Psychologists who study dieting have seen this for decades: one cookie, and the whole day feels ruined, so you might as well eat the whole box. It’s often nicknamed the “what the hell” effect, and it’s all-or-nothing thinking at work.

Streaks can set the same trap. In a series of studies, people were less likely to do something again when their log showed a broken streak rather than an unbroken one, even when what they’d actually done was exactly the same. The number on the screen was doing the damage. The streak is just a counter. The habit lives in the repetitions, and those don’t disappear when you miss a day.

Habits carry you on hard days

Here’s what makes the slow build worth it. When researchers followed students through exam periods, when they were tired, stressed and short on willpower, the students leaned more heavily on their habits. That included the good ones, not only the bad. Stress seems to push all of us toward whatever we usually do.

Willpower tends to run low exactly when life gets hard. A habit is what keeps going when you don’t have the energy to decide. That’s why it’s worth building one on the good days, so it’s there for you on the stressful ones.

Tie it to something that already happens

Habits form around cues: a place, a time of day, or something you already do every day. Instead of deciding to stretch at some point in the morning, decide to stretch for one minute after you switch the kettle on. Every time the cue comes around, it reminds you, and each repetition strengthens the link between the two.

In one trial, tying a new eating or drinking habit, most often drinking more water, to a daily routine worked about as well as tying it to a set time of day, and how often people actually carried out their plan was a key part of success. In a small study of flossing, people who flossed after brushing their teeth built a stronger habit than people who flossed before, and still had it eight months later. Deciding in advance exactly when and where you’ll do something is the idea behind an if-then plan, which is a practical way to make sure those repetitions happen.

Start smaller than you think you need to

Simple behaviors become automatic more readily than complicated ones. In a study of new gym members, the people who went consistently, kept their workouts simple, felt comfortable where they exercised and actually enjoyed it were the ones whose exercise habit grew strongest. Going at least four times a week for about six weeks seemed to be the minimum for a habit to take hold.

The practical version is to make the first step almost too small to skip. It might be one push-up, one page or one glass of water. You can grow it once the link is there, and a small start is much easier to repeat on a bad day. If getting started is the hard part for you, a timer can help with that too.

Make it easy to begin

Small obstacles matter more than we think. Having to find your sneakers, dig out the yoga mat or walk to another room is enough, on a tired evening, to tip the decision the other way. Researchers who study habits suggest making the new behavior as easy to start as possible: the book on your pillow, the water bottle already filled, the running kit laid out the night before.

The time of day may matter

In one small study, students were asked to do the same stretch every day, either just after waking up or just before going to bed. The morning group was estimated to reach automaticity sooner, after about 106 days rather than about 154. It’s one small study, so it’s a hint rather than proof, but it suggests that when you do something can matter as well as how often.

Just don’t make the slot too rigid. When people were paid to go to the gym within a fixed two-hour window each day, they ended up going less, during the study and after it, than people paid to go whenever suited them. A steady cue helps, but a schedule you keep missing doesn’t.

Judge it by effort, not by the calendar

The most useful measure of a habit isn’t the number of days you’ve done it, but how much it takes to start. If the new behavior still needs a decision every time, it isn’t a habit yet. When you notice you’ve done it without having to talk yourself into it, that’s the curve leveling off.

Old habits live in the setting

The same automaticity that makes a new habit slow to build makes an old one hard to break. Because a habit is set off by the situation rather than by a decision, deciding to stop doesn’t reach it very well. That’s why “I’ll just stop” so often fails, and it isn’t a sign of weak willpower.

In one study, students who moved to a new university kept their old habits, like exercising or watching TV, only when parts of the setting stayed the same. When the setting changed, the old habit loosened its grip, and what the students did next sometimes followed what they actually wanted to do much more closely.

A fresh start opens a window

That loosening can be put to use. In a study with about 800 people, a nudge toward greener everyday habits worked better for people who had recently moved than for people who hadn’t. The window seemed to stay open for about three months after the move.

You don’t have to move to get a fresh start. People are more likely to start something new at the beginning of a week, a month or a year, or after a birthday. Researchers call this the fresh start effect: the new date feels like a clean page, and it gives you a little distance from the old version of you. A new job or a new school year can do the same.

Make the old one harder to reach

The flip side of making a new habit easy is making the old one a little harder. If your phone lives on the bedside table, scrolling in bed gets a cue every single night. Charging it in another room takes the cue away. It’s often easier to change the setting than to fight the urge, and those small changes have been studied far less than moving to a new home, but they work on the same idea.

It also helps to give the cue something new to do. If you always reach for a snack when you sit down in front of the TV, decide what your hands will do instead, like making a cup of tea. An empty space is easy for the old habit to fill.

Choose the version you like

Most of the habits we try to build are chosen for what they’ll bring later: better health, better sleep, a finished project. But in a series of studies, how enjoyable something felt in the moment predicted how long people stuck with it, including their New Year’s resolutions, while the benefits they were aiming for didn’t.

When people picked the exercise they enjoyed most rather than the one they thought was most useful, they did more in that workout. And in the eating and drinking trial from earlier, enjoying the new behavior was one of the things that predicted who turned it into a habit. So if you hate running, you’re allowed to dance instead!

Add something pleasant to it

When the habit itself can’t be made more fun, you can add something pleasant to it. In the same research, letting high school students add music, snacks and colored pens to a class assignment kept them working for longer.

One study took this a step further. People were given a gripping audiobook they could only listen to at the gym, and they went to the gym more often, because the story was waiting for them there. The boost faded after a few weeks, so it isn’t magic, but it’s a lovely way to get started. The researchers called it temptation bundling: pairing something you should do with something you want to do.

A podcast you save for the morning walk, a favorite mug for the glass of water, or a friend to meet at the pool are small rewards that arrive today rather than in six months, and they give the next repetition a reason to happen.

A habit isn’t a test you pass on day 21. It’s a curve that keeps rising for as long as you keep coming back to it. So do the small thing again tomorrow, even if you missed it today.