Does Missing a Day Break a Habit? What Studies Found

One missed day costs very little. In the study that measured it, the day after a single miss a habit's automaticity score was lower by 0.29 points on a 0 to 42 scale, and the authors concluded that a missed day "did not materially affect the habit formation process".

Longer gaps are a different matter. The same authors write that missing a week "reduces the likelihood of future performance", and in the check-in records of 60,277 gym members, the longer it had been since the last visit, the less likely the next one was.

This page goes through the studies behind those two statements, one that disagrees in part, and a limit that applies to all of them: people who missed a day and never came back are mostly not in the data.

The evidence at a glance

One missed day

The 2010 study by Lally and others is the one behind the well-known 66-day figure. 96 volunteers each chose a daily behaviour and tried to do it every day for 84 days. Each day they rated how automatic it felt, on a questionnaire scored from 0 to 42.

The researchers picked out single missed days: 140 of them, across 55 people. On the day after a miss, the automaticity score was lower by an average of 0.29 points, which they call "a very small decrease".

They also compared two-day stretches. When the behaviour was done on both days, the score rose by a mean of 0.79 points. When there was a missed day in between, it still rose, by 0.55. So the habit kept growing across a missed day, only a little more slowly.

Two studies with a habit app

A 2021 paper by Stojanovic, Fries and Grund looked at missed days in the logs of a habit app, in two groups.

Study 1: no effect. 91 students at two German universities used the app for six weeks to build a study habit. They logged 2,574 repetitions. Of those, 78.7% came with no day missed since the one before, 13.5% after one missed day and 7.9% after two days or more. The authors found "no effect of not doing one's habit for approximately 1–3 days from time to time".

Study 2: pauses slowed the habit. 196 users of the published app tracked 265 habits. Here 63.7% of repetitions came with no day missed, 15.5% after one day and 20.7% after two days or more. In this group, the authors write, "pausing did slow down automatization".

So the two studies in one paper don't agree, and the group whose logs show more pauses is the one where pauses mattered.

The authors add a warning that applies to both: "these analyses of habit pausing have a survivorship bias as only data from subjects who continued the habit building process after pausing can be included". Someone who misses a day and never opens the app again leaves no later data to analyse. That makes a missed day look safer than it may be.

Not everyone kept logging. Of the 91 students, 57 (62.6%) logged at least 21 repetitions and 27 (29.7%) at least 42.

A missed week

The 2010 authors separate a missed day from a missed week. Pointing to an earlier study of exercise, which we did not open, they sum up: "missing one opportunity does not preclude habit formation, but missing a week's worth of opportunities reduces the likelihood of future performance and hinders habit acquisition".

Gym records point the same way. In a 2023 study of the check-ins of 60,277 regular gym users, for 76% of members the longer it had been since their last visit, the less likely they were to go on a given day. A gap tends to grow.

People who succeed slip too

A study from the 1980s followed 200 people with a New Year's resolution for two years. 77% kept their resolution for one week and 19% for two years. Among those who succeeded, 53% slipped at least once, and the mean number of slips over the two years was 14.

So a slip doesn't mark someone out as failing. A little over half of the people who made it to two years had slipped along the way.

There is also a hint about what helps after a miss. In a test of 54 four-week programmes with 61,293 members of an American fitness chain, the best one offered small rewards for coming back to the gym after a missed workout.

What these numbers can't tell you

• People who quit are missing. The app study says so itself, and the same holds for any analysis of what happens after a miss: it can only follow the people who carried on.
• "Automatic" is self-rated. The 0.29 points come from a daily questionnaire, and 55 people.
• Shares of repetitions. The percentages from the app study are shares of logged repetitions. They are not shares of people or of days.
• Particular groups. The app study describes both its samples as young iPhone users. The students got course credit, and the authors built the app.
• An old study, read in outline. The resolution study is from the United States in the 1980s and relies on what people reported. We read its abstract only.
• No streak counter was tested. None of these studies looked at what seeing a streak reset does to people.

What to do with this

1. After a missed day, do it the next day. One miss cost almost nothing in the study that measured it.
2. Don't let a day become a week. The gap is the risk. Decide in advance what the smallest version of your habit is, so a bad day still counts. How to build a daily streak has examples of minimums.
3. Expect slips. A little over half of the people who kept a resolution for two years slipped at least once.
4. Keep an honest record. If you track a streak, let it reset and start again the same day. A 30-day habit tracker on paper keeps the days you did do in view.

For how long a habit takes in the first place, see how long it takes to form a habit and, for the gym, how long it takes to make exercise a habit. To keep a habit next to the goal it serves, GoalTracker holds your goals and their steps in your browser, free and with no account.

Sources

1. Lally, van Jaarsveld, Potts and Wardle (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology 40(6), 998-1009. doi:10.1002/ejsp.674. Read in full.
2. Stojanovic, Fries and Grund (2021). Self-Efficacy in Habit Building: How General and Habit-Specific Self-Efficacy Influence Behavioral Automatization and Motivational Interference. Frontiers in Psychology 12:643753. doi:10.3389/fpsyg.2021.643753. Open access, read in full.
3. Buyalskaya, Ho, Milkman, Li, Duckworth and Camerer (2023). What can machine learning teach us about habit formation? Evidence from exercise and hygiene. Proceedings of the National Academy of Sciences 120, e2216115120. doi:10.1073/pnas.2216115120. Open access, read in full; supplement not opened.
4. Norcross and Vangarelli (1988). The resolution solution: longitudinal examination of New Year's change attempts. Journal of Substance Abuse 1(2), 127-134. doi:10.1016/s0899-3289(88)80016-6. Abstract only.
5. Milkman and others (2021). Megastudies improve the impact of applied behavioural science. Nature 600, 478-483. doi:10.1038/s41586-021-04128-4. Abstract only.

FAQ

Does missing one day ruin a habit?

Not in the study that measured it. After a single missed day the automaticity score was 0.29 points lower on a 0 to 42 scale, and the authors concluded that a miss did not materially affect habit formation.

Does missing two or three days matter?

The evidence is mixed. In one study of 91 students there was no effect of missing about 1 to 3 days from time to time. In a second group of 196 app users, pauses slowed the growth of the habit. Both analyses leave out people who stopped for good.

What happens if I miss a week?

The authors of the 2010 study write that missing a week's worth of opportunities reduces the likelihood of future performance and hinders habit acquisition. In gym records, the longer since the last visit, the less likely the next one.

Do people who keep their resolutions ever slip?

Yes. In a two-year study of 200 people, 53% of those who succeeded had slipped at least once, and the mean number of slips was 14.

Should I start again after breaking a streak?

Yes, and on the same day if you can. The studies here suggest that the size of the gap matters more than the miss itself.