The 21/90 rule

It takes 21 days to create a habit.

It takes 90 days to create a lifestyle.

In the mid of last century, Maxwell Maltz, a plastic surgeon noticed a strange pattern among the patients he was treating. When he would perform an operation he found that it would take the patient about 3 weeks to get used to the new thing. Researching further, Maltz noticed that it also takes about 21 days to form a new habit. He made sure to say that this was the minimum amount of time needed to adapt to a new change. In 1960, Maltz published a book called Psycho-Cybernetics, which sold millions of copies.

In the years that followed, Maltz’s work influenced many self-help professionals like Brian Tracy, Zig Ziglar Tony Robbins etc. People began to say “It takes 21 days to form a new habit” instead of “It takes a minimum of 21 days to form a new habit”.

Phillippa Lally, a health psychology researcher in London examined the habits of 96 people over a 12-week period and published the results in the European Journal of Social Psychology. Lally and her research team decided to figure out just how long it actually takes to form a habit.

In the study, each person chose one new habit for a period of 12 weeks and reported each day on whether or not they did the behavior and how automatic the behavior felt. Some people chose simple habits like “drinking a bottle of water with lunch.” Others chose more difficult tasks like “running for 15 minutes before dinner. 

At the end of the 12 weeks, the researchers analyzed the data to determine how long it took each person to go from starting a new behavior to automatically doing it. Phillippa Lally and the team found that on an 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. So, the truth is that it will probably take you anywhere from two months to eight months to build a new behavior into your life — not just 90 days as the 21/90 rule says.

Finally, how long it takes to form a particular habit doesn’t really matter that much. Whether it takes 90 days or 365 days, you have to put in the work.

The only way to get to Day 365 is to start with Day 1. So forget about the number and focus on doing the work.