How long does it take to form a habit? 66 days, not 21

Around New Year’s or the start of a semester, you’ve probably heard that if you can just stick with something for 21 days, it becomes a habit. That number is said to have spread from Maxwell Maltz, a plastic surgeon who wrote in the 1960s that it took patients “a minimum of about 21 days” to get used to their new faces. It didn’t come from a study that measured habits. So how long does it take to form a habit?

When researchers measured it: 66 days

In a study published in 2010, a team led by Phillippa Lally at University College London (UCL) had 96 participants each pick one new behavior, like “eat a piece of fruit with lunch” or “run for 15 minutes before dinner,” and do it every day. For 84 days, participants recorded daily how automatic the behavior felt.

It took a median of 66 days for that sense of automaticity to level off and stop rising. The time varied widely by person and behavior, from 18 to 254 days. This figure is based on the 39 participants whose data fit the model well, though, so treat it as a rough guide rather than an exact deadline.

A 2024 review by Australian researchers, which pooled 20 studies on habit formation, found something similar. Among the studies that reported how long habit formation took, the median was 59–66 days and the mean was 106–154 days, and individuals took anywhere from 4 to 335 days.

So if it still feels hard after three weeks, you haven’t failed; that’s perfectly normal. It’s more realistic to give it two months and not be surprised if it takes longer.

Missing a day is fine

The UCL study had one more finding worth noting. Missing a single day had almost no effect on habit formation. People who skipped often, though, didn’t form the habit.

When a 30-day streak breaks, it can feel as if everything has fallen apart, and many people quit altogether. But what builds a habit isn’t an unbroken streak; it’s how many times you’ve done it. If you miss a day, just pick it back up the next day.

How to build habits that last

Attach it to something you already do

Habits become automatic when you repeat the same behavior in the same situation. Tie a new habit to something you already do every day, like “after breakfast” or “after I brush my teeth,” and you won’t have to think about when to do it.

Start small

“Ten squats after dinner” will last longer than “an hour of exercise every day.” Once the small version is automatic, build on it.

Stick to two or three

When you start several habits at once, one slipping can bring them all down. Start with two or three, and add a new one only after one of them has lasted more than a month.

It doesn’t have to be every day

For habits that are hard to keep up daily, like exercise, pick specific days, such as three times a week. When only those days count, your rest days don’t go down as failures.

Keep a visible record

When your progress piles up on a monthly calendar, you notice the filled-in days before the empty one. Jot down a line even on days you skip, and later you’ll be able to see why you slipped.

Try it with Haruda Ritual

Haruda Ritual is a habit tracker that stacks your habits on a calendar instead of a checklist. Track habits five ways (daily check, times per day, minutes per day, times per week, and minutes per week), and if you choose specific weekdays, only those days count. Even if a streak breaks, the dots on your calendar stay, and you can fill in missed days later.