📆The median time to form a habit in one study was 66 days

In a 2010 study by Phillippa Lally and colleagues at University College London, 96 volunteers each chose one small daily behaviour and reported for twelve weeks how automatic it felt. For those whose data fitted the model, the median time to reach a plateau of automaticity was 66 days.

The number everyone repeats is the 66. The real finding is the spread: 18 to 254 days, depending on the person and the behaviour. The study also found that missing a single day did not noticeably damage the process.

Why I kept it: three weeks is folklore and 66 days is a midpoint, not a promise. I plan for months now: 💎 A habit takes months and not three weeks. My reading notes are in 📖 Lally on how long a habit takes.

What the number cannot carry

• One study, 96 people, self-reported.
• A median: half the participants took longer.
• The upper figures are extrapolated from fitted curves, since the study itself ran for 84 days.
• Drinking a glass of water became automatic much sooner than exercise did.

Where I found it: 🔬 How are habits formed - Modelling habit formation in the real world.