A prominent study by Phillippa Lally and colleagues at University College London, published in the European Journal of Social Psychology, tracked participants as they adopted new habits. The researchers found that, on average, it took 66 days for a new behavior to become automatic.
Other systematic reviews, including a 2024 PMC meta-analysis, support this average but also highlight substantial individual variation, with some people forming habits in as little as 18 days and others taking up to 335 days. The 66-day figure represents a median, not a minimum or maximum.
The UCL study and corroborating research debunk the popular belief in a universal 21-day timeline and emphasize that habit formation is a process shaped by personal, behavioral, and contextual factors.
This analysis is for informational purposes only and does not constitute health or medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making health-related decisions.