66 days to build a habit: what the study really found

In a 2009 University College London study, habits took a median of 66 days to feel automatic, with a range of 18 to 254. Missing one day did not derail progress.

The short version: try one today

• Plan for about ten weeks.
• Do not restart the count after a miss.
• Pick a simple habit. Simple ones formed faster.

Keep forgetting the new routine? Priori has reminders and streaks to keep it in front of you. (We make it. It's free to download.)

You have probably seen the claim that a habit takes 21 days. It is tidy, it fits on a mug, and it has made a lot of people feel broken on day 22. The better known research figure is 66 days to build a habit, and even that number is more interesting, and kinder, than the headline suggests.

What the study really found

In 2009, researchers at University College London followed people as they tried to make a new daily behaviour automatic. Automatic here means you do it without having to argue with yourself first. The median time to reach that point was 66 days.

The median is the middle of the group, so half took longer. The full range ran from 18 days to 254 days. That is a gap of most of a year between the fastest and the slowest person, all doing ordinary small habits.

Two other findings matter if you have ADHD. Simple habits formed faster than complicated ones. And missing one day did not derail progress. People who skipped a day and came back ended up in much the same place.

One honest caveat. The study looked at adults in general, and it did not focus on people with ADHD. So treat 66 as a rough guide to the scale of the job, and expect your own number to land anywhere in that wide range.

Plan for ten weeks, and expect the middle to be boring

Sixty-six days is roughly ten weeks. That is longer than a 30 day challenge and shorter than a university term. Planning for ten weeks changes how you set things up, because you stop relying on the first rush of enthusiasm to carry you.

Say you want to take your make-up off before bed. Week one is easy because it is new. Weeks three to six are the dull stretch, where it still takes effort and no longer feels exciting. Put your supports there. Leave the cleanser next to your toothbrush, set a labelled alarm, tell a flatmate.

It also helps to know that slow is normal. If you are on day 40 and still have to remind yourself, you are well inside the range the study found. There is more on realistic timelines in habit formation takes longer than the internet says.

Why you should never restart the count

Many women with ADHD describe an all or nothing streak. You miss Tuesday, decide the whole attempt is ruined, and plan to start fresh on Monday. Then Monday becomes the first of next month.

The study gives you permission to drop that rule. A missed day was a missed day and nothing more. So keep counting from where you were. Day 23, a gap, day 25. The repetitions you already did still count.

If a tracker that shows a broken chain makes you want to quit, change the tracker. Count total days done instead of days in a row. You can read more about that in planning for the break in a streak.

Using 66 days to build a habit that is small enough

Simple habits formed faster, so size is the lever you control. The version you pick should be doable on a day when you are tired, late and slightly annoyed.

• Drink a glass of water with breakfast, instead of 'drink more water'.
• Put tomorrow's clothes on the chair, instead of 'have a full evening routine'.
• Open your calendar when you sit down at work, instead of 'get organised'.
• Walk to the end of the road after lunch, instead of 'exercise daily'.

You can grow it later. For the first ten weeks the only job is repeating one small thing in the same spot in your day until it stops needing a decision. On some weeks that will feel harder, and many women report that focus and energy shift across the menstrual cycle. Keep the habit tiny enough to survive those weeks too.

Quick questions

Does it really take 66 days to form a habit?

Sixty-six days was the median in a 2009 University College London study, so it is a middle point and not a rule. People in the study took anywhere from 18 to 254 days. Simple habits tended to become automatic sooner.

If I miss a day, do I have to start the 66 days again?

No. The study found that missing a single day did not derail progress. Pick up where you left off and keep going.