The popular belief that forming a new habit only takes 21 days stems from Maxwell Maltz's 1960 observations, not rigorous scientific research. Maltz, a plastic surgeon, noted some of his patients took about three weeks to adjust to changes, but he never conducted formal studies on habit formation.
Contemporary research, such as the 2024 systematic review published on PMC and the University College London (UCL) study, finds that the average time to form a new habit is 59–66 days, with some individuals taking as little as 4 days and others as long as 335 days. The 21-day figure is not supported by any scientific data.
Caltech researchers and the American Council on Science and Health (ACSH) have explicitly debunked the 21-day claim, clarifying that habit formation is highly individual and depends on factors like the complexity of the behavior and personal motivation. Relying on the 21-day myth may set unrealistic expectations for people trying to adopt new habits.