When the researchers examined the different habits, many of the participants showed a curved relationship between practice and automaticity of the form depicted below (solid line). On average a plateau in automaticity was reached after 66 days. In other words it had become as much of a habit as it was ever going to become.
This graph shows that early practice was rewarded with greater increases in automaticity and gains tailed off as participants reached their maximum automaticity for that behaviour.
Although the average was 66 days, there was marked variation in how long habits took to form, anywhere from 18 days up to 254 days in the habits examined in this study. As you'd imagine, drinking a daily glass of water became automatic very quickly but doing 50 sit-ups before breakfast required more dedication (above, dotted lines). The researchers also noted that:
Missing a single day did not reduce the chance of forming a habit.
A sub-group took much longer than the others to form their habits, perhaps suggesting some people are 'habit-resistant'.
Other types of habits may well take much longer.
it takes two months on average to form a habit
