How to use it
- Enter the date you started the habit, or the date you plan to start.
- Read the three dates: the fastest result in the study, the average and the longest estimate.
- Check the timeline to see which day you are on today.
Free tool
Habit formation calculator
Enter the day you started a new daily habit. See where you are against the milestones from the best-known study on how long habits take to form.
Day 18 · Fastest in the study
The quickest anyone reached their plateau. Usually a very simple habit.
Day 66 · The average
The average time for a daily behaviour to reach its automaticity plateau.
Day 254 · Longest estimate
The slowest estimated plateau. Bigger habits can take most of a year.
Where the numbers come from
In a 2009 study at University College London, Phillippa Lally and colleagues asked volunteers to repeat a new healthy behaviour every day in the same context, such as drinking water with lunch or a short exercise routine, and to rate how automatic it felt.
Automaticity rose quickly at first and then levelled off. The average time to reach that plateau was 66 days, and the range ran from about 18 days to an estimated 254 days.
How to read your dates
These are milestones from one study, not a prediction for you. Simple habits tend to settle faster than demanding ones, and doing the habit at the same time and place each day helps.
The same study found that missing a single day did not materially affect the process. So if you slip, the rule is simple: never miss twice. Our guide on how long it takes to form a habit goes deeper.
FAQ
Questions
Not usually. The 21-day figure is a popular myth. In the study behind this calculator the average was 66 days, with a wide range.
Not necessarily. 66 days was the average plateau in one study. Yours may be sooner or later depending on the habit and how consistently you repeat it.
No. The study found that one missed day did not materially affect habit formation. Get back to it the next day.
No. The calculator runs in your browser and sends nothing to us.
Keep going
Related
Paper is a great start
When you want reminders, streak freezes and friends keeping score, Streako is free on Android.