Think It Takes 21 Days to Form a Habit? Science Says Think Again

A popular piece of self-help folklore might be more complicated than we thought. New research finds that it takes significantly more than a month for a new habit to form.

Scientists at the University of South Australia conducted the study, a review of the existing evidence on habit forming. They found that habits typically begin forming after about two months. For some unlucky people, though, it could even take up to a year.

With 2025 still fresh off the stove, there are undoubtedly lots of people who have begun a new exercise regimen or other healthy lifestyle change in recent weeks. And you might have heard that it takes 21 days for a routine to start becoming engrained into our lives; others might have heard 18 or 28 days instead. Some studies, however, have suggested that this supposed rule isn’t quite so simple.

To get at the root of this topic, the University of South Australia researchers analyzed data from 20 studies that examined the forming of healthy habits like routine exercise, drinking water, or flossing teeth; these studies collectively involved over 2,500 participants. One specific question these studies sought to answer was how long it took for a habit to reach something called “automaticity”—the point at which people perform it regularly and without too much thought being put into it.

The researchers found that habits formed around 106 to 154 days on average. The median length of a habit forming was roughly 59 to 66 days (the median is the midpoint in a group of numbers in case you forgot). That said, the study did reveal plenty of outliers. The shortest reported length of habit adoption was four days, while the longest was a whopping 335 days.

“Emerging evidence on health-related habit formation indicates that while habits can start forming within about two months, the time required varies significantly across individuals,” the researchers wrote in their paper, published last month in the journal Healthcare.

The researchers say they were only able to find a relatively small number of studies to analyze, and most of the studies included were judged to have a high risk of potential bias. So more and better quality studies are needed to better understand the duration and other aspects of habit forming, they say.

At the same time, the researchers believe their findings should reassure people who are feeling discouraged about not having adapted to their new routine or habit as quickly as they would expect from the popular wisdom. They also note that there are science-backed ways to improve the odds of a lifestyle change sticking.

“When trying to establish a new healthy habit, success can be influenced by a range of things including how frequently we undertake the new activity, the timing of the practice, and whether we enjoy it or not,” said lead study researcher Ben Singh in a statement from the university. “If you add a new practice to your morning routine, the data shows that you’re more likely to achieve it. You’re also more likely to stick to a new habit if you enjoy it.”

I’m personally very encouraged by that advice, given my new healthy habit this year of rubbing my face into my cat’s belly every morning.