“It takes exactly 21 days to form a new habit.”

Four studies reported the median or mean times to reach habit formation, ranging from 59–66 days (median) and 106–154 days (means), with substantial individual variability (4–335 days). The meta-analysis showed significant improvements in habit scores pre- to post-intervention across different habits (standardised mean difference: 0.69, 95% CI: 0.49–0.88).

It takes an average 66 days to form a new habit, according to new research by Phillippa Lally and colleagues from the Cancer Research UK Health Behaviour Research Centre based at UCL Epidemiology and Public Health. The team has completed a groundbreaking investigation into how people form habits, published last month in the European Journal of Social Psychology.

Researchers found that new habits can begin forming within about two months (median of 59-66 days) but can take up to 335 days to establish. Dr. Ben Singh from the University of South Australia, who led the research, stated, that "the adoption of healthy habits is vital for long-term health and well-being, but forming these habits and breaking away from old unhealthy habits can be difficult."

Results indicated that habit formation increased substantially over the course of three months, especially for participants who consistently performed the desired behavior during this time. Habit strength increases steeply at first, and then levels off. Although some people manage to form certain habits as quickly as 18 days, others need as much as half a year.

It was once believed that a habit forms after 21 consecutive days—a notion popularized by surgeon and writer Maxwell Maltz in “Psycho-Cybernetics... From these rather anecdotal observations, Maltz proposed that it takes a minimum of 21 days... Maltz's conclusions, based solely on his clinical observations, not rigorous clinical trials or cohort studies, made his claims scientifically unsound. The results showed that: Automaticity plateaued at 66 days, with individual variation ranging from 18 to 254 days.

A popular claim suggests habits can form in 21 days, but research shows this timeline varies widely depending on the behavior, individual, and context. Healthy eating habits required a median of between 59 and 66 days to form, although not all participants reached the level of automaticity. For self-reported habits, such as healthy eating and stretching, the time to habit formation varied from 91 to 154 days.

Scientists at the University of South Australia conducted a 2025 review of existing evidence on habit forming, analyzing data from 20 studies involving over 2,500 participants. They found that habits typically begin forming after about two months, with the median length of habit forming being roughly 59 to 66 days, and a range from four days to 335 days.

A 2010 study followed volunteers trying to build simple routines and found it took a median of 66 days for the behaviour to become automatic. Recent reviews, including one in 2025, found that habit formation took between 59 and 154 days on average, with some taking as few as four days and others nearly a year, highlighting that habit formation isn't one-size-fits-all.

According to an older study, it takes 18 to 254 days for a person to form a new habit. But other studies have reported that, on average, it can take 66 days for a new behavior to become automatic. According to a 2024 systematic review, emerging evidence suggests that it can take approximately 2 months (around 60 days) to form a new habit.

"There is no magic number for habit formation," says Anastasia Buyalskaya (PhD '21), now an assistant professor of marketing at HEC Paris. "You may have heard that it takes about 21 days to form a habit, but that estimate was not based on any science," Camerer says.

A new study from scientists at the California Institute of Technology found that there's no one timeline for forming a habit, and it varies widely depending on the task at hand. For example, forming a gym habit took an average of about six months, while health-care workers got into the habit of frequent hand-washing in just a few weeks, debunking the idea that it takes exactly 21 days.

PSA: The 21-Day Habit Is a Myth... the 21-day habit-forming timeframe isn’t exactly rooted in science. According to a 2012 review of the psychology of habit formation, the concept originates from anecdotal evidence of cosmetic surgery patients who reported adjusting to their new appearance at the 21-day mark... Researchers find that it takes around 66 days on average to adopt a new healthy habit, but even still, they report “considerable variation across participants and behaviors.”

On average, it takes more than 2 months before a new behavior becomes automatic — 66 days to be exact. And how long it takes a new habit to form can vary widely depending on the behavior, the person, and the circumstances. In Lally's study, it took anywhere from 18 days to 254 days for people to form a new habit. The idea that it takes 21 days to form a new habit originated from Dr. Maxwell Maltz's observations in the 1950s, which were later misinterpreted.

The 21-day claim originated from Dr. Maxwell Maltz's 1960 book 'Psycho-Cybernetics,' where he observed that patients took about 21 days to adjust to physical changes like new facial features after surgery. This anecdotal observation was misinterpreted and popularized as a universal rule for habit formation, despite lacking empirical support.