Habits take about 66 days, and missing a day is fine

What we know

When you start something new, how long does it take before it feels like second nature? The best-known study that actually measured this comes from Phillippa Lally and colleagues at University College London (2010).

96 people in the UK each chose one new behavior related to eating, drinking or physical activity, and did it every day in the same situation, for example “after breakfast”. For 84 days, they recorded whether they did it and how automatic it felt, meaning how much it happened without thinking.

The results:

• The median time for automaticity to level off was 66 days.
• But people differed enormously, from 18 to 254 days. (Values beyond the study period were predicted from each person’s curve.)
• Missing a single opportunity had little effect on forming the habit.
• On the other hand, people whose performance was very inconsistent did not form a habit.

The 66-day figure comes from the 39 participants whose data fitted the curve well.

Building on this work, Benjamin Gardner and colleagues from the same group wrote a guide for family doctors (2012) on how to help patients form habits. The core advice: repeat a chosen behavior in response to the same cue, in the same situation. At first you do it deliberately. With repetition, it moves into a stage where it continues with little effort.

How to read it

Lally’s study observed 96 people over 84 days. It was not an experiment that randomly assigned conditions. Automaticity was self-reported, and each person picked a different behavior. So 66 days does not mean “everyone forms a habit in 66 days”. It is the middle value among these participants.

Two points matter most:

1. Not having a habit after a few weeks is not failure. In this study, it was common for people to need more than two months.
2. Missing one day does not reset you to zero. But when misses pile up and your pattern becomes erratic, the habit is less likely to form.

A set of US experiments on streaks (Silverman and Barasch, 2023) found that showing people that their streak was “broken” made them less likely to continue the behavior. The effect was stronger when people felt the break was their own fault. And in a large US study of more than 60,000 gym members (Milkman and colleagues, 2021), out of 54 different approaches, offering a small reward for returning after a missed workout produced the biggest increase in gym visits.

A small step for today

• Pick one cue. Tie your habit to something that happens every day, like “move for 5 minutes after my morning coffee”.
• Decide when and where. The habit “decided when and where to do tomorrow’s most important task” follows the same idea.
• The day after a miss, do it just once. Research suggests one missed day has little effect, so put your energy into coming back. The day you return is the most important one to log.
• Use 66 days as a rough checkpoint. After a little over two months, look back and ask whether it now feels natural.

Sources

• [E1] Lally et al. (2010) How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology.
• [E2] Gardner, Lally & Wardle (2012) Making health habitual: the psychology of ‘habit-formation’ and general practice. British Journal of General Practice.
• [E5] Silverman & Barasch (2023) On or Off Track: How (Broken) Streaks Affect Consumer Decisions. Journal of Consumer Research.
• [A10] Milkman et al. (2021) Megastudies improve the impact of applied behavioural science. Nature.