The 66-day habit challenge
The 66-day habit challenge comes from a 2010 University College London study that found it took a median of 66 days for a new daily habit to feel automatic. The challenge is simple: pick one small habit, do it every day for 66 days, ideally with a friend. DuoShare has a built-in 66-day challenge you can start in one tap.
Where 66 days comes from
Phillippa Lally and colleagues followed 96 people who each picked a new daily behavior, like drinking water with lunch or running before dinner. They measured how automatic it felt each day. On average it took 66 days to plateau, with a huge range of 18 to 254 days depending on the person and the habit. Simple habits stuck faster; harder ones took longer. Missing a single day did not meaningfully set people back.
Source: Lally, van Jaarsveld, Potts and Wardle, “How are habits formed,” European Journal of Social Psychology, 2010.
The three phases
- Days 1–21: the honeymoon and the dip. Motivation is high, then fades around week three. This is where most people quit.
- Days 22–45: the grind. The habit is not automatic yet and not new anymore. A partner matters most here.
- Days 46–66: it starts to feel normal. Skipping feels strange instead of tempting.
Make it work
- Pick something small enough to do on your worst day.
- Attach it to something you already do: after coffee, after brushing teeth.
- Do it with a friend so the dip in week three has someone on the other side.
- Allow imperfection. The research found one missed day did not ruin habit formation. DuoShare’s N/A day exists for the same reason.
The 66-day reset in DuoShare
DuoShare includes a 66-day reset: six small daily habits, side by side, with a milestone card at each stage and a finish card at day 66. You can also turn any habit into a 66-day challenge and invite up to 3 friends for free.
DuoShare at a glance
- What it is
- An accountability habit tracker for iPhone: you and your friends check off goals and see when each other is done.
- Price
- Free. Goals, friends, streaks, reminders, the widget and challenges with up to 4 people cost nothing.
- DuoShare Pro
- Optional: groups and challenges of 5 to 10 people. $29.99 once, or $4.99 a month.
- Platform
- iPhone (iOS). No Android or web app yet.
- Challenges
- 7, 30 or 66 days, with one friend or a group, joined with one link.
- Streaks
- Your streak grows every day you check off a goal. Mark a goal N/A once a week without breaking it.
- Sharing
- Every milestone becomes a card you can post to Instagram, Messages or anywhere.
- Privacy
- Goals are private until you share them with friends you choose. Nothing is public. Your journal is never shared.
- Languages
- English and Spanish.
- Made by
- SearchWrite LLC, United States.
Start in under a minute
- Get DuoShare free on the App Store and sign up with your phone number.
- Add one to three small goals. Small sticks.
- Send a friend your invite link. Your streak starts with your first check-in.
iPhone · Free · No ads
Questions
Does it really take 66 days to form a habit?
66 days was the median in Lally’s 2010 study, but individual results ranged from 18 to 254 days. Simple habits form faster; harder ones take longer.
Is the 21-day rule true?
No. The 21-day idea comes from a 1960 book by plastic surgeon Maxwell Maltz about how long patients took to adjust to changes. It was never a study of habit formation.
What if I miss a day during 66 days?
Keep going. The research found a single missed day did not significantly affect the habit forming. DuoShare lets you mark a goal N/A once a week.
Is there an app for the 66-day challenge?
Yes. DuoShare has 66-day challenges built in, free on iPhone.