Metabolic Health
Habits and Consistency
Most of us have heard it takes 21 days to build a habit. In the best-known study on this, it took 66 days on average, and some people took a lot longer. This article covers where the 21 days came from, what the research found, what happens when you miss a day, and how to pick one habit and make it stick.
In the best-known study, 96 adults each picked one healthy habit to do every day for 12 weeks, and it took 66 days on average before it felt automatic. One person got there in 18 days, and others were still working on it when the study ended. A 2024 review of 20 studies found about two months as well.
There's some truth in it. The first few weeks take the most effort, and it gets easier after that. But 21 days doesn't tell the whole story. The number comes from a book a plastic surgeon wrote in 1960. He noticed his patients took about three weeks to get used to their new face.
In the study that followed people for 12 weeks, missing a single day didn't set people back. Missing a lot of days did. So if you miss one, do it the next day. You don't need to wait for Monday or start over.
Tie it to something you already do every day and do it right after, like a glass of water once your morning coffee is poured. Keep it small enough to do on a bad day. In a study on flossing, people who flossed right after brushing tended to build a stronger habit than people who flossed before.
In one study, adults trying to lose weight got a short list of habit tips and a daily checklist. After eight weeks they had lost about 4½ pounds. The group still waiting for the tips lost about 1. Results vary person to person.
Most of us have heard that it takes 21 days to build a habit. The number comes from a book a plastic surgeon named Maxwell Maltz wrote in 1960. He noticed his patients took about three weeks to get used to their new face.
He was writing about getting used to a change, and that's a different thing from doing something new every day until it's automatic. Somewhere along the way, his number turned into a rule for habits, and it's been repeated ever since.
There's some truth in it. The first few weeks are the hardest, and it does get easier after that. But 21 days doesn't tell the whole story. When researchers followed people building a new habit, it usually took about two months.
So if it isn't 21 days, how long does it take? In the best-known study on this, from University College London, 96 adults each picked one healthy habit, like eating a piece of fruit with lunch, going for a 15-minute run before dinner, or doing 50 sit-ups after their morning coffee. They were asked to do it every day right after the same thing, and every day they rated how automatic it felt. The study ran for 12 weeks.
From a study of 96 adults who each picked one new daily habit. The bar runs from day 0 to day 90.
On average it took 66 days before the new habit felt automatic. One person got there in 18 days, and others were still working on it when the 12 weeks ended. Simple habits got there sooner. Exercise habits took about one and a half times as long as eating or drinking habits.
A 2024 review pulled together 20 studies with 2,601 people. In the four studies that timed it, the typical time was 59 to 66 days, and some people took as few as 4 days and some as many as 335. Habits done in the morning, and habits people picked for themselves, tended to be stronger.
A habit is something you do without having to decide to. It forms when you do the same thing at the same point in your day, like right after your morning coffee or as soon as you get home from work. Do it enough times and the coffee starts to remind you on its own.
The shape of the average in the study: easier fast at first, then leveling off. It's drawn to show the shape, not one person's numbers.
That's why the first few weeks take the most effort. In the study, it got easier fast at first, then more slowly, until it leveled off. If week three still feels like work, that's normal. Most people aren't there yet.
Two we hear a lot: "I already blew it today, so I might as well keep going" and "I'll just start over tomorrow." Here's what the research found about missed days. In the 12-week study, missing a single day didn't set people back. Missing a lot of days did.
So if you miss a day, do it the next day. Don't wait for Monday and don't start over. One missed day doesn't undo your progress.
The same goes for food. If you ate something you didn't plan to, the next meal is the place to pick back up. You don't have to wait until tomorrow.
So how do you choose? Start with the basics: water, walking, exercise, sleep, or tracking your calories. Pick the one that would help you most right now, and pair it with something you already do every day.
Two more studies show why the pairing matters. In one, people who were told to floss right after brushing their teeth tended to build a stronger flossing habit than people told to floss before. In the other, researchers pooled 94 tests of people planning exactly when and where they'd do something ("after I pour my coffee, I'll drink a glass of water"), and the people who planned it that way were more likely to follow through.
Keep it small enough for a bad day. Ten minutes of walking, not an hour. If you'd skip it on your worst day, make it smaller. It also helps to set things up ahead of time, like the water bottle on the counter or your walking shoes by the door. If walking is the one you pick, the walking article covers how to build up from where you are now. If it's sleep, start with the sleep article.
They can. In one study, 104 adults trying to lose weight took part. Some got a short leaflet of simple habit tips for eating and activity, plus a daily checklist to tick off. The rest were on a waiting list for the same tips. After eight weeks, the group with the tips had lost about 4½ pounds, and the group still waiting had lost about 1. After eight months, about a quarter of the people who got the tips had lost 5 percent or more of their weight. Results vary person to person.
I would rather see someone walk ten minutes after dinner every day than do one hard workout a week and nothing in between.
Pick one habit from the basics and pair it with something you already do every day. Make it small enough for a bad day, and if you miss a day, do it the next day. Give it about two months before you judge it. If you'd like help picking the one that will make the biggest difference for you, a clinician-supervised weight-loss program at Optimized Health starts with a comprehensive clinical evaluation, and at your first visit we go over what you eat and drink on a normal day. At follow-ups we check on the one habit you're working on before we add another. We see patients in Joplin and by telehealth in MO, KS, IA, UT, and WA. Results vary person to person. Consistency over intensity.
Where this comes from: the 12-week habit study is Lally and colleagues, European Journal of Social Psychology, 2010; the review of 20 studies is Singh and colleagues, Healthcare, 2024; the 21-day figure is from Maxwell Maltz, Psycho-Cybernetics, 1960; the flossing study is Judah and colleagues, British Journal of Health Psychology, 2013; the planning review is Gollwitzer and Sheeran, Advances in Experimental Social Psychology, 2006; the weight-loss study is Lally and colleagues, International Journal of Obesity, 2008. Full citations are in the campaign claims register.
If you'd like help picking the one habit that will make the biggest difference for you, schedule a visit. At your first visit we go over what you eat and drink on a normal day.
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