How Long Does It Take to Build a Habit? (Hint: Not 21 Days)
Short answer: On average about 66 days, but anywhere from 18 to 254 days in the best-known study (Lally et al., 2009). The popular "21 days" figure is a myth. A 21-day challenge is still useful, as a trial sprint rather than a finish line.
You've heard it a hundred times: it takes 21 days to build a habit. Plenty of apps and books are built around that number, including some we list. It's a nice round figure. It's also not what the research says.
Where does the 21-day habit rule come from?
The number traces back to Maxwell Maltz, a plastic surgeon who wrote Psycho-Cybernetics in 1960. He noticed that patients took about 21 days to get used to a new appearance after surgery, and that people who lost a limb needed a similar stretch to adjust. He described it as a minimum, a rough observation. Over the decades, "at least 21 days" quietly became "21 days and you're done".
What does the research say about habit formation?
Phillippa Lally and colleagues at University College London published a study in the European Journal of Social Psychology (online in 2009, in print in 2010). They followed 96 volunteers for 12 weeks as each tried to make one new daily behaviour automatic, such as eating fruit with lunch or running before dinner.
The results were messier than 21:
- The median time to reach automaticity was 66 days.
- The range was huge: 18 days to 254 days.
- Simple habits (drinking a glass of water) formed faster than complex ones (50 sit-ups).
- Missing a single day did not noticeably derail the process.
That last finding is the most useful. A broken streak isn't failure. It's a bump.
So is a 21-day challenge pointless?
No, it's just mislabelled. Three weeks is long enough to learn whether a habit fits your life and short enough that you won't be bored before you start. Treat day 21 as the end of the first sprint.
A challenge works best when you:
- Pick one habit. Not five.
- Make it small enough to be easy. BJ Fogg, who directs the Behavior Design Lab at Stanford and created the Tiny Habits method, recommends starting with a version so tiny it feels silly: flossing one tooth, doing two push-ups.
- Anchor it to something you already do. "After I pour my morning coffee, I will write one line in my journal."
- Plan for the miss. Decide in advance that a skipped day just means you go again tomorrow.
- Keep going past day 21 if it still takes effort. The research says two months is typical.
Do habit tracker apps work?
A tracker won't build the habit for you, but it does three useful things: it reminds you, it shows your streak, and it makes your pattern visible on days when your memory says "I never do this".
From their App Store listings, the two habit apps we feature work like this:
- 21 Days Habit Transformation is built around a 21-day challenge. It offers a streak tracker, workout log, water tracker, goal planner and progress stats, works offline, and is available in 32 languages.
- Habit Tracker: Goal Calendar lets you create custom habits, plan a daily routine, set reminders and see progress reports, with calendar integration and widgets.
Both are free to download, and the listing for the 21-day app mentions a Pro subscription. They're also new to the store: each has a single rating so far, which isn't enough to judge how they hold up over months. If you try one, leave an honest review after a few weeks.
The 21-day app's listing says science shows habits lock in after 21 to 30 days. Given the research above, we'd read that as a rough guide, and plan for longer.
A simple plan to try
- Day 1: pick one habit, shrink it, attach it to an anchor and add it to your tracker.
- Days 2 to 21: do the tiny version and mark it done. If you miss, carry on the next day.
- Day 22: ask whether it feels automatic. If yes, add a second habit. If not, keep the first one going for a few more weeks.
A good first habit to try is a ten-minute weekly money check, which fits neatly with our budget routine. Looking for tools? Our guide to habit tracker and daily planner apps compares them.
Related reading
Sources and further reading
- Lally, van Jaarsveld, Potts & Wardle, "How are habits formed: Modelling habit formation in the real world", European Journal of Social Psychology (2010)
- BJ Fogg: Tiny Habits
Frequently asked questions
Does it really take 21 days to form a habit?
No. The 21-day figure comes from a 1960 book's casual observation. A 2009 University College London study found it took a median of 66 days, with a range of 18 to 254.
What happens if I miss a day?
Probably nothing. The same study found that missing a single day didn't materially affect habit formation. What matters is getting back to it the next day.
What is the best habit tracker app for iPhone?
It depends on what you want to track. Compare streaks, reminders, calendar sync and widgets, and check the free tier first. Both apps in our library are new with few ratings, so try the free version before paying.
How do I stay consistent with a new habit?
Start tiny, tie it to an existing routine and track it somewhere visible. Make the first version so easy that skipping it feels harder than doing it.
21 Days Habit Transformation
Habit Tracker: Goal Calendar