You may have heard that it takes just 21 days to make a new habit stick.
Where did this idea come from? And is it true?
It began more than 60 years ago, when a US cosmetic surgeon, Dr Maxwell Maltz, published a wildly popular and influential self-help book called Psycho-Cybernetics.
Among Dr Maltz’s observations on human behaviour, he noticed his patients took about 21 days to get used to their new faces.
He also reported that amputees took 21 days to adjust to the absence of a limb – which he said was the same amount of time most people take to get used to a house they had moved into.
Getting used to something new isn’t the same as establishing a new habit – and Dr Maltz’s rule was based on patient reports, not hard science – but somehow the idea took hold.
Common sense tells us
Three weeks is an easy sell. It feels doable. But common sense suggests it’s not right.
For all the years that the ’21 days’ theory has thrived in pop culture, millions of people failed to swap a poor diet for a healthy one, or to engage in regular exercise.
Many haven’t tried, and never will.
And of those who tried, most struggled and failed to make healthy practices a habit.
Of course, it’s bound to be difficult. The bottom line: Forming a habit takes time.
Scientists are working on it
The study considered to be “seminal” in the science of habits, and how long they take to be made or broken, didn’t happen until 2009.
The University College London study recruited 96 volunteers who wanted to change a specific behaviour. Performing the behaviour was tied to a daily cue such as eating breakfast.
One volunteer managed to make his new habit an automatic behaviour, but most volunteers needed much longer, some needing 254 days.
The average was 66 days.
Some habits take longer than others
In a new study from Caltech, 30,000 gym-goers were tracked over four years, with their gym visits recorded.
Data analysis found that it took an average of six months for gym-going to become an automatic behaviour.
Similarly, more than 3000 healthcare workers were tracked over nearly 100 shifts, with their episodes of hand-washing recorded.
It took the healthcare workers an average of “a few weeks” to automatically wash their hands, as they need to do, several times a day.
Colin Camerer is a professor of behavioural economics from the University of Chicago, and co-author of the new paper. He said: “You may have heard that it takes about 21 days to form a habit, but that estimate was not based on any science.
“Our work supports the idea that the speed of habit formation differs according to the behaviour in question and a variety of other factors.”
Other factors
The study is the first “to use machine learning tools to study habit formation”.
The researchers employed machine learning to “analyse large data sets of tens of thousands of people who were either swiping their badges to enter their gym or washing their hands during hospital shifts”.
Machine learning allowed the researchers to observe “hundreds of context variables that may be predictive of behavioural execution”.
Short version: The researchers were able to identify if, for example, attending the gym at a certain time helped or hindered habitual attendance.
In fact, time of day had “no effect on gym habit formation”.
Whereas, for 76 per cent of gym-goers, “the amount of time that had passed since a previous gym visit was an important predicator of whether the person would go again”.
In other words, the longer it had been since a gym-goer last went to the gym, the less likely they were to make a habit of it.
And 69 per cent were “more likely to go to the gym on the same days of the week, with Monday and Tuesday being the most well attended”.
Bottom line: There is no magic number in how long it will take you to make that new habit you’ve been dreaming about.
