Free tool

How long will my habit take to form?

Tell the calculator how hard the habit is, how fixed its cue is and how many days a week you do it. It gives you a realistic range of days until the habit is likely to feel automatic, built around the best-known study on the question, where the median was 66 days.

Drink water quest art from XP Tracker, Hunter version

Your habit

How hard is the habit?

Simple. One small action, like a glass of water with breakfast or taking a vitamin. Medium. A few minutes and a little effort, like ten minutes of reading or a short walk after lunch. Harder. Real effort or time, like a workout, an hour of study or a cold shower.

How fixed is the cue?

Same time and place every day, straight after something I already do. Mostly the same, with some days that look different. No fixed cue yet. I fit it in when I can.

Days per week The study looked at daily habits. Fewer days a week usually means more calendar days.

Start dateToday, or the day you began.

Where the numbers come from

Phillippa Lally and her colleagues at University College London asked 96 volunteers to pick one new daily habit, such as drinking water with lunch, eating fruit or going for a run before dinner. For 12 weeks the volunteers reported each day whether they did it and how automatic it felt. The study appeared online in 2009 and in the European Journal of Social Psychology in 2010.

For the people whose data fitted a clear curve, the time to reach the plateau of automaticity ranged from 18 to 254 days. The median was 66. Automaticity rose fastest in the early weeks and then levelled off. Simple habits, like drinking water, got automatic sooner than harder ones, like exercise. And missing a single day did not materially set anyone back.

Physical Training quest art from XP Tracker, Hunter version — Exercise habits tended to take longer to feel automatic than simple ones.

How the calculator works

The study gives one median and one spread. It does not give a formula for your habit. So the calculator starts at 66 days and adjusts it with three planning factors we chose to reflect what the study and common sense suggest:

middle guess = 66 × difficulty × cue × days per week

Factor	Options and values
Difficulty	simple 0.8, medium 1, harder 1.35
Cue	same time and place 0.9, mostly 1, no fixed cue 1.25
Days per week	7 days 1, 6 days 1.1, 5 days 1.25, 4 days 1.45, 3 days 1.75

The range runs from 0.6 to 1.8 times the middle guess, never below the study's 18 days, rounded to the nearest 5. A medium habit with a mostly stable cue, done daily, comes out at about 40 to 120 days. These factors are educated guesses. They are useful for planning, and they are not findings.

How to use your range

Plan for the late end. If you expect the habit to feel easy by day 21, a normal day 30 will feel like failure. If you expect up to 120 days, day 30 feels like progress.
Make the cue fixed before you make the habit bigger. Of the three inputs, the cue is the one you control today. The if-then planner helps you write one.
Don't restart the count after a missed day. Carry on from where you are. The streak calculator shows your consistency, which is the better measure.

Your next step: write the date at the late end of your range in your calendar, with a note to check how automatic the habit feels by then.

Questions people ask

How long does it take to form a habit?

In the study by Lally and colleagues (2010), new daily habits took between 18 and 254 days to reach their plateau of automaticity, with a median of 66 days. Simple habits got there faster than harder ones. There is no single number that fits everyone. The full answer is in our guide on how long it takes to form a habit.

Is it true that a habit takes 21 days?

No study found that. The figure goes back to Maxwell Maltz's book Psycho-Cybernetics (1960), where he wrote that people needed a minimum of about 21 days to get used to changes such as a new face after surgery. Over time "a minimum of about 21 days" turned into "21 days". See the 21-day myth.

How long does it take to form a habit of working out?

Usually longer than a simple habit like drinking a glass of water. In Lally's study, exercise habits tended to take longer to become automatic than eating and drinking habits. Choose "Harder" in the calculator, and keep the workout's start, such as putting on your shoes at the same time each day, as fixed as you can.

What if I miss a day while forming a habit?

Keep going. Lally's study found that missing one day did not materially affect the process. Long gaps are a different story, so aim to come back the next day.

How do I know when a habit has formed?

The habit starts when you do it in its usual situation without having to decide to. Lally's team measured this with questions like whether the person did it automatically and without thinking. If you would feel odd skipping it, it is probably close.