Many people believe that it only takes 21-days to form a habit. If this were true, then every 21-days, you’d be rewiring your brain to prefer a healthier diet, crave exercise, automatically tune-out your favorite guilty-pleasure, and achieve just about every single goal you routinely fail to achieve.
There’s a good chance that if you’ve attempted to make any of these changes, that you struggled, failed in your first attempt, tried again and failed again, and then maybe if you kept at it, after several months to a year, you finally nailed it.
Despite the popular misconception, there is no substantial evidence that habits are routinely formed in just 21-days. This is a popular myth, circulated by self-help gurus, that has inspired a massive number of people to build habit apps, that claim to transform people’s lives in just 21-days.
If you go to the Journal of Medical Internet Research (, which has a large collection of scientific peer reviewed papers on habit forming apps, you’ll quickly realize that behavioral scientists don’t talk about the 21-day habit cycle, but rather, the myth is being perpetuated by self-help gurus.
So, at this point you may be asking, how long does it take to form a habit? Although there are not that many studies focused exclusively on quantifying the time, one study, called “How are habits formed”, found that the average person formed a habit in 66 days, which we can rounded to 2-months, as a decent ballpark figure.
What the study showed, is that if you carry out a routine behavior every single day, that it will start to feel more automatic every day, and by about 2-months, it will feel completely automatic, which is the point at which, you’d say a habit was formed.
The authors also found that cheat-days didn’t have any long-term damage on habit formation, provided someone gets back on the program the day after. However, cheat-weeks did slow down the habit formation process.
From my own experience, there appears to be a scientific trend (that I have not systematically evaluated) that successful behavior change programs tend to run for approximately 2-months, and that after this point, there is a large drop in adherence and impact. The big statistical meta-analysis that I carried out a few years back (, showed that online programs lasting more than 4 months, all failed. So as a rule of thumb, for most general purposes, 8-weeks is not a bad approximate time duration for many programs.
However, depending on the behavior and audience, you might be able to get away with 6-weeks, or need to add extra time, especially if you’re trying to make an impact on highly engrained behaviors. I recommend that you research each specific behavior, target user groups, and then pilot to figure out the timing, content, and program, before you bother hitting a line of code.
But no matter how long your program, the real trick to forming habits, is getting people to stick with your program, and not dropout. Scientists call this “adherence”, which is key, because most people who stick with viable programs, get the results. But the problem is that most people stop using habit forming technologies long before their habits can form.
So if you want to start building habits, start with a realistic timeframe (about 8-weeks), develop a strategy to keep people engaged, and do what you can to re-engage people who drop out all the time, and pull them back on the bandwagon.


  • Lally, P., Van Jaarsveld, C. H., et al. (2010). “How are habits formed: Modelling habit formation in the real world.” European Journal of Social Psychology 40(6): 998-1009.
  • Eysenbach, G. (2005). The law of attrition. Journal of medical Internet research7(1).
  • Cugelman, B., Thelwall, M., & Dawes, P. (2011). Online interventions for social marketing health behavior change campaigns: a meta-analysis of psychological architectures and adherence factors. Journal of medical Internet research13(1).

This article is part of series, on the top-10 misleading claims in digital psychology.

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