Anyone who has tried to build a new habit knows the feeling of breaking the chain. A missed morning walk or a skipped glass of water can seem to undo weeks of effort, and many people give up at that point. A study from University College London suggests that reaction is misplaced. Missing a single opportunity to perform a new behavior did not significantly affect how quickly it became a habit. On average, it took 66 days for a new daily habit to feel automatic.

That finding sits alongside other research suggesting that consistency over the long run may depend less on never slipping and more on having plans that can bend. Studies of exercise incentives and of goal setting have found that some built-in flexibility helped people keep going after the initial push faded.

How long a habit takes

The UCL study, led by Phillippa Lally and published in the European Journal of Social Psychology, followed 96 people over 12 weeks. Each chose one new behavior to perform daily. Some picked something simple, such as drinking a bottle of water with lunch. Others chose something harder, such as running for 15 minutes before dinner.

Every day, participants reported whether they had performed the behavior and how automatic it felt, using statements such as “I do this without having to consciously remember.” The researchers tracked how long it took for that sense of automaticity to level off.

According to UCL’s announcement of the findings, the average was 66 days. The individual range was wide. As writer James Clear notes in a summary of the study, it ran from 18 days to an estimated 254 days, with the longest figures projected from the 12-week data rather than directly observed.

The 66-day figure is often quoted as if it applies to everyone. The study itself was small, and the spread of results suggests that the time a habit takes depends heavily on the person and the behavior.

What a missed day does

The part of the study most relevant to everyday life concerns slips. The researchers reported that “missing one opportunity did not significantly impact the habit formation process.” A day off did not reset the clock.

There was a limit. People who were very inconsistent, missing the behavior often, did not go on to form habits. The finding suggests not that consistency is unimportant, but that an occasional lapse is not the setback it can feel like at the time.

That distinction matters because of how people tend to respond to a lapse. If a single miss feels like failure, it is tempting to abandon the effort altogether. If it is understood as a normal part of building a habit, it becomes easier to simply resume the next day.

When rigid routines backfire

A large field experiment at Google tested a related question: is it better to build a habit at a fixed time each day or to allow flexibility? John Beshears of Harvard Business School and colleagues, publishing in Management Science, enrolled 2,508 Google employees who had access to on-site gyms.

Each participant chose a two-hour window on weekdays as their ideal exercise time. Some were then paid only for 30-minute workouts that started within that window. Others were paid the same amount for working out at any time. A control group received encouragement but no payment. The incentives ran for four weeks.

According to Harvard Business School’s account of the study, the two paid groups went to the gym about equally often while the payments lasted. After the money stopped, both groups dropped off, but by different amounts. Those who had been paid only for their fixed window became 10 percentage points less likely to visit the gym at least once a week. Those who had been paid for any time fell by 5 points.

Beshears said the researchers were “absolutely surprised” that flexibility did better for longer-term habit formation. One plausible reading is that people who could only earn a reward at a set time missed out entirely when their schedule shifted, while those with flexibility found other ways to fit exercise in.

Building in a few spare days

Research on goal setting points the same way. Marissa Sharif of the Wharton School and Suzanne Shu of UCLA’s Anderson School of Management have studied what they call emergency reserves: a small number of permitted skips built into a demanding goal.

In one study, described in UCLA Anderson Review’s summary of the work, more than 270 students and staff were set a daily step target 20% above their usual level for a month. Some had an easy goal of reaching it five days a week. Some had a hard goal of seven days. Others had the seven-day goal but with two skip days a week, or eight across the month.

Participants with the reserve days reached their goals up to 40% more often than those with either the easy or the hard goals, and took more steps overall. They were also more likely to get back on track after a miss: 55% of those with weekly reserves met their goal the day after missing it, compared with 37% of those with the strict seven-day target.

The researchers suggest two reasons. Labeling the skips as emergency reserves made people reluctant to use them, so they kept trying. And when a miss did happen, it felt less like failure, turning, in the authors’ words, “a sense of failure into a sense of progress.”

What the research cannot say

These studies have limits. The UCL study involved fewer than 100 people and relied on their own sense of how automatic a behavior felt. The Google experiment involved workers at a single company with on-site gyms, and it measured gym visits rather than other forms of exercise. The goal-setting experiments ran over weeks rather than years, and several used games or short challenges.

Together, though, they suggest that perfection is not a requirement for consistency. A missed day did not undo a forming habit, flexible routines outlasted rigid ones once incentives ended, and goals with a little slack kept people going after a slip. For anyone trying to build a lasting habit, the more useful aim may be returning quickly after a lapse rather than never having one.

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