Every January, gyms fill up. By February, most of the new faces are gone. If you’ve ever been one of them, it probably wasn’t a lack of willpower. It may have been a bad number.
Don’t approach your health through New Year’s resolution intervals of three weeks on, and forty-nine weeks off.
Caleb O. Pinegar, D.O., A.T.C., UNSPLODE
Where “21 days” came from
The idea that a habit takes 21 days traces back to Psycho-Cybernetics, a 1960 book by Dr. Maxwell Maltz, a plastic surgeon. He noticed that patients seemed to need at least about three weeks to get used to a change, like a new face after surgery. That’s getting used to something, not building a habit. Researchers at University College London have described the 21-day rule as unfounded as a basis for habit formation.
What the research actually says
In 2010, Phillippa Lally and colleagues at University College London published one of the first real-world studies of how habits form. Participants picked a daily health behavior, like drinking water with lunch or doing sit-ups, and tracked it for 84 days.
- On average, it took about two months for the behavior to feel automatic.
- The range was enormous: from 18 days to a predicted 254 days.
- Simple behaviors, like drinking water, became automatic faster than harder ones, like exercise.
- Missing one day had little effect on progress.
A larger 2023 study in the Proceedings of the National Academy of Sciences used machine learning to follow more than 30,000 gym-goers over four years and more than 3,000 hospital workers’ handwashing. Handwashing became a habit in a few weeks. Going to the gym took about six months. As lead author Anastasia Buyalskaya put it, “There is no magic number for habit formation.”
That matches what I wrote in the book:
Converting old habits into new ones is hard. It takes months, sometimes longer.
Caleb O. Pinegar, D.O., A.T.C., UNSPLODE
Why short programs fade
A 2021 “megastudy” in Nature tested 54 different four-week programs designed to get 61,293 gym members to work out more. While the programs ran, 45% of them increased gym visits. Once the support ended, only 8% still showed a measurable effect.
The lesson isn’t that programs don’t work. It’s that four weeks is too short for most people, and support matters long after the first burst of motivation.
How to make a habit stick
1. Start smaller than feels impressive
Pick something you can do on your worst day, not your best one. Build from where you are, and add to it only once it feels routine.
2. Make it a habit goal, not a checkbox goal
A checkbox goal has a finish line, and once you cross it, it’s easy to slide back. In the book I put it simply:
Replace “checkbox” goals with habitual goals.
Caleb O. Pinegar, D.O., A.T.C., UNSPLODE
Instead of “lose twenty pounds,” aim for a weekly standard you keep, like “walk four mornings a week.”
3. Plan for the miss
You will miss a day. The research says that’s fine. What matters is the next day. Decide ahead of time what “coming back” looks like, so a miss doesn’t turn into a month off.
4. Surround yourself with people who already do it
The people around you shape your health habits more than most of us admit. I call it an achievement contagion:
the achievement contagion is probably the only condition I’ve listed in this book that I hope you do catch.
Caleb O. Pinegar, D.O., A.T.C., UNSPLODE
5. Judge it in months, not weeks
Check in at two months and again at six. If the habit is easier than it was, it’s working, even if it isn’t automatic yet.
One small step
Pick one habit that would protect your HealthSpan. Write it as a weekly standard, not a finish line. Then put a date on your calendar two months from today to check in.
- Use the goal builder in the free Health Portfolio worksheet.
- Read Healthspan vs. lifespan: the 12-year gap for why it matters.
This article is general education, not medical advice. Talk with your own physician before you start a new exercise or nutrition routine.
About the author
Caleb O. Pinegar, D.O., A.T.C.
Caleb O. Pinegar, D.O., A.T.C., is an orthopedic surgeon at C.O.P. Orthopedics and co-author of UNSPLODE. He wrote the HealthSpan side of the book.
From the book UNSPLODE: The Bold New Approach to Reconstruct Your WealthSpan and HealthSpan. Read both introductions free.
Sources
- Lally P, van Jaarsveld CHM, Potts HWW, Wardle J. “How are habits formed: Modelling habit formation in the real world.” European Journal of Social Psychology, 2010 (summary, British Psychological Society Research Digest)
- UCL Health Behaviour Research Centre blog on the 21-day myth and Maltz’s Psycho-Cybernetics
- Buyalskaya A, et al. “What can machine learning teach us about habit formation? Evidence from exercise and hygiene.” PNAS, 2023
- Neuroscience News, “There Is No Magic Number for Habit Formation” (on Buyalskaya et al.)
- Milkman KL, et al. “Megastudies improve the impact of applied behavioural science.” Nature, 2021 (summary, Scimex)