Phillippa Lally is a health psychology researcher at University College London. In a study published in the European Journal of Social Psychology, Lally and her research team decided to figure out just how long it actually takes to form a habit.
The study examined the habits of 96 people over a 12-week period. Each person chose one new habit for the 12 weeks and reported each day on whether or not they did the behavior and how automatic the behavior felt.
Some people chose simple habits like “drinking a bottle of water with lunch.” Others chose more difficult tasks like “running for 15 minutes before dinner.” At the end of the 12 weeks, the researchers analyzed the data to determine how long it took each person to go from starting a new behavior to automatically doing it.