Count the days you did it, not the days since you started. A missed day doesn't move the marker.
UCL study, 2010: 18 to 254 days, median 66
Review of studies, 2024: 4 to 335 days
What the research found
18 to 254 days, median 66
In a UCL study, 96 volunteers, mostly university students, each chose an eating, drinking or activity behaviour to do daily in the same context for 12 weeks. For the 39 people whose data fitted the model well, the median time to reach 95% of their automaticity plateau was 66 days, ranging from 18 to 254 days. The study ran for 84 days, so the longest times (up to 254 days) were projected from each person's curve, not observed.
4 to 335 days across studies
A 2024 review of 20 studies (2,601 people, health behaviours) found four that reported how long habits took: median times of 59–66 days and averages of 106–154 days, with individual times from 4 to 335 days. 11 of the 20 studies had a high risk of bias.
Why your number may differ
How long a habit takes differs depending on who you are and what you are trying to do. So the chart shows where your days sit on the ranges, and nothing more: no date and no prediction.
Where “21 days” comes from
The "21 days" figure traces back to Maxwell Maltz's 1960 book Psycho-Cybernetics, which said it usually takes "a minimum of about 21 days" to see a change in a mental image. He drew it from patients getting used to a change after plastic surgery, not from research on forming habits.
Count the days you do it
The habit tracker counts your total days done, and a missed day never takes anything away. Starting from scratch? Make a habit plan with a tiny version and a cue.
If you need help now
These tools are for everyday habits. They are not a crisis service. If you are struggling or don't feel safe, you can contact:
988 Suicide & Crisis Lifeline
988 Suicide & Crisis Lifeline (US): call or text 988, or chat online. Free and confidential, 24/7.
Emergency services (911)
US: call 911 if you or someone you know is in immediate harm or danger.
Samaritans
Samaritans (UK and Ireland): call 116 123, free, 24 hours a day, 365 days a year.
Emergency services (999 or A&E) · NHS 111, mental health option
UK: call 999 or go to A&E if someone's life is at risk or you can't keep yourself or someone else safe. For urgent help that isn't an emergency, call 111 and choose the mental health option (NHS).
Elsewhere, call your local emergency number.
Sources
- 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 40:998–1009. doi:10.1002/ejsp.674
- Gardner B, Meisel S (2012). Busting the 21 days habit formation myth. UCL Health Behaviour Research Centre blog. blogs.ucl.ac.uk
- Singh B, Murphy A, Maher C, Smith AE (2024). Time to Form a Habit: A Systematic Review and Meta-Analysis of Health Behaviour Habit Formation and Its Determinants. Healthcare 12(23):2488. mdpi.com
- 988 Suicide & Crisis Lifeline. 988 Suicide & Crisis Lifeline. 988lifeline.org
- Contact Us. 988 Suicide & Crisis Lifeline. 988lifeline.org
- Contact a Samaritan. Samaritans. samaritans.org
- Where to get urgent help for mental health. NHS. nhs.uk