Do you really need 21 days to build a habit?

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We all want to make lasting changes to our daily behaviors from time to time — perhaps exercise more or spend less time scrolling through social media before getting out of bed. But how long does it take to build a habit? 

A popular answer is 21 days — a figure that can be traced back to Dr. Maxwell Maltz, a cosmetic surgeon and author of "Psycho-Cybernetics" (Prentice-Hall, 1960). In his book Maltz reported that his patients needed a minimum of 21 days to change the mental image of how they looked.

Since then, many people have applied the "21-day" time frame to all habits. However, not all behaviors are the same and some may need more than three weeks to become automatic. 

"It is easy to see why this figure appeals," Mark Vahrmeyer (opens in new tab), a psychotherapist and founder of Brighton & Hove Psychotherapy (opens in new tab) in England, told Live Science. "It is both concrete and makes building a new habit seem very achievable. The truth, however, is that it's more complex and on average it takes far longer."

So is there a precise time frame that it takes to form a habit? To answer this question, we took a dive into the science of habit formation.

What is a habit?

A habit is a behavior that has become automatic, according to a 2019 article published in the Oxford Research Encyclopedia (opens in new tab). Habits can be formed and eliminated deliberately or unintentionally. We may not even be aware of some of these behaviors. 

Dr Maurice Duffy (opens in new tab), a mindset coach and visiting professor of innovation and entrepreneurship at the University of Sunderland, England, told Live Science that habits play a central role in determining our actions.

"Habits are the small decisions you make and the actions you perform every day," he said. "Your life today is essentially the sum of these habits."

But these habits aren't always conscious decisions. Habit is different from routine.

"A habit is a behavior done with little or no thought," Duffy said. "A routine involves a series of behaviors [performed] frequently and intentionally repeated. Unlike habits, routines are uncomfortable and require a concerted effort to change. Habits, on the other hand, are so ingrained in our daily lives that it feels strange not to do them." 

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Not all habits are beneficial or practical, and some may be harmful. 

This is because habit formation doesn't occur in the prefrontal cortex — the "reasonable," decision-making part of the brain. A 2006 review article published in the journal Nature Reviews Neuroscience (opens in new tab) suggests that the ability to develop and maintain habits may be rooted in basal ganglia. Basal ganglia are clusters of neurons, or nerve cells, located deep in the brain, underneath the white matter. They are central to emotional development, pattern recognition, problem solving and learning. This could explain why certain behaviors take place without any decision-making process, and why some behaviors may be linked to emotional states like stress or sadness. 

How long does it take to build a habit?

Repetition is critical to habit formation. "Habits are formed through a process known as habituation," Alyssa Roberts (opens in new tab), an eating disorder researcher at the University of Minnesota,  told Live Science. "Habituation occurs when a behavior is repeated enough times, and the brain adapts to the routine by making the response automatic."

The "habit loop" concept, popularized by journalist Charles Duhigg (opens in new tab) in his book "The Power of Habit" (Random House Trade Paperbacks, 2014), is often used to explain the science of habit formation. According to the theory, there are three stages to automating your behavior: cue (or trigger), routine (or behavior) and reward. 

For example, a stressful situation (a cue) may lead some people to respond with overeating (the routine), which is an activity that can temporarily bring some comfort (the reward). When a behavior becomes sufficiently repetitive, the brain starts viewing the cue as an opportunity for the reward. The trigger will prompt you to perform the same action to seek pleasure. 

How long it takes to establish a habit may depend on what the cue and the intended routine is. According to a 2009 study published in the European Journal of Social Psychology (opens in new tab), habit formation may take anywhere between 18 and 254 days. The average amount of time needed for a behavior to become automatic is 66 days, the researchers found. The researchers noted that different actions required a different level of effort too. For example, those who had been asked to develop a habit of drinking a glass of water at breakfast tended to be more successful than participants who were instructed to do 50 sit-ups each day. 

How do you maintain a habit?

Maintaining a habit long-term can be tricky. According to a 2016 review in the journal Health Psychology Review (opens in new tab), many different factors play a role in achieving lasting behavior change. These include personal motives, physical resources, ability to self regulate one's behavior and a range of environment and social influences. Biological factors may also have an effect. 

"Genetics can play a role, as some people are genetically predisposed to forming habits more quickly than others due to their dopamine receptor genes," Roberts said. As stated in a 2007 review in The Journal of Neuroscience (opens in new tab), dopamine is a brain signaling molecule that plays an essential role in the early stages of learning. Increased dopaminergic activity can speed up the process of habitualization.  

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A 2016 review, published in the journal Health Psychology (opens in new tab), suggested that self-efficacy could also be key to developing and maintaining habits. Self-efficacy is a belief in your ability to complete a task or achieve a goal. Put simply, a person who is convinced they cannot maintain new behaviors will be less likely to keep their habit. Higher self-efficacy has been linked to improved outcomes in many different health interventions, according to a 2016 review in the journal Health Education & Behavior (opens in new tab). Participants who exhibited this trait tended to be more successful at giving up smoking, losing weight, reducing alcohol consumption and increasing physical activity. 

Vahrmeyer noted that the way a person makes a goal more attractive can also be important.

"If the process of building your habit involves nothing but self-sacrifice with no reward, you are unlikely to stick to your goals," Vahrmeyer said.

He advised making the process as easy as possible. For example, if the goal is to go to the gym three times per week, a person should pick a gym with a convenient location. 

Habit formation can also be made more satisfying.

"Perhaps you approach the latter by celebrating milestones along the way and rewarding yourself with a gift linked to the new habit,” said Vahrmeyer.

Anna Gora
Health Writer

Anna Gora is a health writer at Live Science, having previously worked across Coach, Fit&Well, T3, TechRadar and Tom's Guide. She is a certified personal trainer, nutritionist and health coach with nearly 10 years of professional experience. Anna holds a Bachelor's degree in Nutrition from the Warsaw University of Life Sciences, a Master’s degree in Nutrition, Physical Activity & Public Health from the University of Bristol, as well as various health coaching certificates. She is passionate about empowering people to live a healthy lifestyle and promoting the benefits of a plant-based diet.