Count new habits in months, not in "21 days"

Cost

Free. What it takes is repeating the same action every day in the same setting for several months.

What you get

96 volunteers each chose one action to do with eating, drinking or activity, and did it every day in a fixed setting (for example, "after breakfast") for 12 weeks, rating how automatic it felt each day. The data of 82 people were good enough to analyze, and the model was fitted successfully for 62 people. The number of days needed to reach 95% of each person's own automaticity ceiling ranged from 18 days to 254 days. The study also found that missing one chance to do it made no real difference to how the habit formed.

Notes

This is only one study, with 96 people, all doing simple actions (for example, eating a piece of fruit after a meal). No one has measured how long complex things take, such as running three times a week or writing every day. So it is not evidence of failure if it still takes a lot of effort after two weeks. To make the repetition actually happen, tie the action to a fixed setting; see §4.1 (write it as "at this time, in this place, when this happens, I do that").

Evidence grade

B : Supported by research but without a precise number, or based on small or single studies.

Sources

1. Lally P, van Jaarsveld CHM, Potts HWW, Wardle J (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998–1009. https://doi.org/10.1002/ejsp.674

Translated from the Chinese original. Original book, section 4, tip 12. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer