MEPX
Chapter 2 of 10All chapters
  1. 1What a habit is
  2. 2How long it takes
  3. 3Starting a habit
  4. 4Implementation intentions
  5. 5Environment
  6. 6Breaking a habit
  7. 7Lapses
  8. 8Rewards and tracking
  9. 9Identity and goals
  10. 10Honest limits

Chapter 2 of 10

How long it takes

Not 21 days.

The real number

The most cited study found a median around 66 days, ranging from 18 to 254 depending on the person and the behaviour. Complexity and frequency both matter.

  • The 21 day figure comes from a plastic surgeon's 1960 observation about patients, not from habit research.
  • Drinking water becomes automatic far faster than exercising does.

The curve

Automaticity rises steeply at first and then flattens. Early repetitions matter most, which is why consistency in the first weeks pays off disproportionately.