Habit formation: how habits are formed

When psychologists say “habit,” they mean something narrower than the everyday word. Benjamin Gardner, Phillippa Lally and Jane Wardle, writing for family doctors, define habits as actions “triggered automatically in response to contextual cues that have been associated with their performance” (Gardner, Lally and Wardle, 2012). Their example is washing your hands after using the toilet. The toilet is the cue, washing is the action, and after enough repeats you no longer decide to do it.

Wendy Wood and David Neal, two psychologists who have studied habits for years, describe the same thing from the inside (Wood and Neal, 2007). In their account, a habit grows out of links learned slowly between an action and what surrounds it when you do it: a place, a time of day, or the action that came just before. Once the habit has formed, being in that situation is enough to set off the action, with no goal having to step in first.

The last part of that line is what separates a habit from something you merely do often, or a goal you are working toward. You can go running three times a week by planning every run. A habit is when getting home and changing into your running shoes happen together, with no debate in between.

Habits are worth understanding because so much of an ordinary day runs on them. When Wood, Quinn and Kashy had students keep hourly diaries, somewhere between a third and a half of what the students did counted as habit, repeated almost daily in the same place (Wood, Quinn and Kashy, 2002). Gardner and colleagues add that habits are “cognitively efficient”: once an action runs by itself, your attention is free for something else (Gardner, Lally and Wardle, 2012).

The idea most people meet first is the habit loop, from The Power of Habit, a popular book by the journalist Charles Duhigg (Duhigg, 2012). Duhigg describes a habit as a loop with three parts. A cue tells your brain which habit to run, the routine is the behavior itself, and the reward tells your brain whether this loop is worth remembering for next time.

Duhigg built the loop from research he reported on, in particular experiments in Ann Graybiel’s lab at MIT, where rats learned a maze until running it became automatic. Graybiel’s own review of that work describes how all kinds of routines become habitual through learning, with circuits deep in the brain, called the basal ganglia, taking a large part (Graybiel, 2008).

The loop is a fair summary, with one caution. It is a story told by a writer who read the research, not a finding from a single study, and studies measure its parts in different ways. What they back most clearly is the first part, the cue, and what repeating an action after it does over time.

Every account of habit formation comes back to one recipe, and the researchers who wrote it up for doctors put it in a line: repeat an action consistently in the same context (Gardner, Lally and Wardle, 2012). Each time the cue and the action happen together, the link between them grows a little stronger, until the cue starts the action before you have decided anything.

The clearest measure of how long that takes comes from a study by Phillippa Lally and colleagues at University College London. They asked 96 volunteers to pick one new daily eating, drinking or exercise habit, such as a glass of water after breakfast, and to do it after the same cue for 12 weeks. Every day, each volunteer rated how automatic the behavior felt (Lally and colleagues, 2010).

The ratings climbed quickly at first, then slowed, then leveled off, the way a curve flattens as it nears its ceiling. For the people whose ratings followed that shape clearly, the median time to reach the flat part was 66 days, and single habits took anywhere from 18 to 254. A later review of 20 studies put the usual time for health habits at 2 to 5 months (Singh and colleagues, 2024).

Two other findings from the Lally study change how a bad week should feel. Missing one chance to do the behavior did not really affect how the habit formed, so a missed evening is not a restart. And simple actions got there sooner than longer routines. The full numbers, and a countdown to your own day 66, are on how long it takes to form a habit.

What “automatic” feels like

Researchers measure a habit by asking how automatic it feels, using four plain statements from a short questionnaire (Gardner and colleagues, 2012). The statements are: I do it automatically, I do it without having to consciously remember, I do it without thinking, and I start doing it before I realize I’m doing it.

Early on, you have to remember the habit and talk yourself into it. Later, you notice you have already started. The shelf where the book lives, or the shoes by the door, has taken over the job of reminding you.

Habituation sounds like the process of forming a habit, and many people search for it meaning exactly that. In psychology, though, it names a different kind of learning: getting used to something that keeps happening, until you stop reacting to it.

The classic description comes from a 1966 paper by Richard Thompson and William Spencer, two neuroscientists who listed the features habituation shows across many animals (Thompson and Spencer, 1966). In 2009, a group of researchers led by Catharine Rankin met to update that list, and they define habituation as a drop in a response that comes from repeated stimulation and is not simply tired senses or tired muscles (Rankin and colleagues, 2009). It is often called the simplest form of learning.

You know it from ordinary life. A new clock ticks loudly on the first night and is silent by the end of the week, though the clock has not changed. The first buzz of a new phone makes you look; a month later you barely hear it. If the sound stops for a while and then returns, it tends to catch you again, which the researchers call spontaneous recovery.

So if you searched for habituation because you want an action to become automatic, the part you want is how a habit forms, above. If you wanted to know why you stopped noticing a sound, a smell or a buzz, habituation is the right word. The two can sit side by side in one evening: you stop noticing the buzz of the phone, and you still pick it up the moment dinner ends.

A habit has formed when it stops getting more automatic, not when a set number of days has passed. The practical test is the four statements above. Rate each one from 1 to 7 once a week, and the habit has settled when the score sits above the middle of the scale and stops rising. The self-check on how long it takes to form a habit asks the four questions and keeps your weekly scores in your browser.

The minutes are the part people get wrong: “I read most evenings” can turn out to be two. A good way to track a habit counts the minutes from what you already write or say about your day, with no timer to start. Most journaling apps stop at how the day felt, not where it went, so a habit's real minutes never add up anywhere you can compare.

One app built for this is Think in Numbers, a smart journaling app with time tracking built in.

You write or say your day in your own words, as it happens or all at once. The app reads what you wrote and counts the hours that went to each part of it: the minutes your habit got, what it replaced, your phone, and the time you never mentioned (shown as unaccounted). Then it shows those hours over days and weeks. Habits keep their streaks and reminders, and insights over weeks show whether the minutes are holding.

Write my first day

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A habit is a cue and an action that have happened together often enough to run on their own. Pick one cue you meet every day, keep it steady, make the action small and pleasant, and expect weeks of repeats, not days.

Choose tonight’s cue now. The repeats start the first time you meet it.

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