Expect a habit to take two months, or much longer
In a review of health habit studies, the four that measured it reported medians of 59 to 66 days and averages of 106 to 154 days for a habit to form, with people ranging from 4 to 335.
A new health habit often takes two months or more to form, and the range from person to person is wide.
The study
This review gathered 20 studies of health habits such as physical activity, drinking water, flossing, and healthy eating. Only four of them reported how long habits took to form, and those put the median at 59 to 66 days and the average at 106 to 154 days, with individuals ranging from 4 to 335 days. Most of the included studies were rated at high risk of bias, so the authors treat the evidence as early. Across the studies, habit strength did improve after the interventions. Morning habits and habits people chose for themselves tended to be stronger.
Starting small
Two months or more is a rough guide, not a finish line. A habit you picked yourself, done at a steady time such as the morning, gives it a good chance to settle in.