How long does it take to form a habit? Not 21 days

Usually around two months, and often much longer. In a widely cited study that tracked people building a new daily habit, the median time to reach near-maximum automaticity was 66 days, and individuals ranged from 18 to 254 days (Lally et al., 2010). A 2024 review of 20 studies with about 2,600 participants found medians of 59 to 66 days, averages of 106 to 154 days, and individual times anywhere from 4 to 335 days (Singh et al., 2024).

So no, there is no 21-day rule. But short goals still have a job to do, as long as you treat them as checkpoints rather than a finish line.

Where “21 days” came from

The number traces back to Psycho-Cybernetics, a 1960 self-help book by the plastic surgeon Maxwell Maltz. Drawing on what he saw in his patients — getting used to a new face after surgery, for instance — he wrote that it takes “a minimum of about 21 days for an old mental image to dissolve and a new one to jell.” Over decades of retelling, an observation about self-image became a promise about forming any habit, and “a minimum of about” quietly fell away. No formal experiment was ever run to test it (Scientific American).

What the research found instead

Lally and colleagues asked 96 volunteers to pick one new daily behavior — something to eat, drink or do, in the same situation each day — and to rate every day for 12 weeks how automatic it felt. For most people, automaticity rose quickly at first and then leveled off, like a curve flattening toward a ceiling. The 66-day figure is the median point where people got close to their own ceiling (95% of it). The researchers could only fit that curve for some participants, and the longest times are projections past the study’s 12 weeks — which is itself a sign of how slow some habits are.

Three things in that research are more useful than the headline number:

• Early repetitions count the most. Because the curve is steepest at the start, the first few weeks do a lot of the work, even though the habit won’t feel effortless yet.
• Simple behaviors tend to get there faster. The 2024 review concluded that simpler, repetitive behaviors with clear cues are easier to automate. A study of millions of real-world records found the same split: hospital handwashing became habitual in weeks, going to the gym took months (Buyalskaya et al., 2023).
• Consistency of context matters. Doing the behavior in the same situation is what lets that situation start to trigger it. A habit that moves around your day has a harder time attaching to anything.

How to tell a habit is forming

Counting days tells you how long you’ve been at it. Automaticity tells you whether it’s sticking. Researchers measure it with short questionnaires (Gardner et al., 2012) whose items translate into questions you can ask yourself:

• Do I do it without having to consciously remember?
• Do I start before I’ve really decided to?
• Once I’m in the situation, does it happen without much thought?

If the honest answer is still “no” at day 21, nothing has gone wrong. That’s what the research predicts.

Use a short goal as a checkpoint

A first target of one, three or four weeks is still worth setting. It’s close enough to feel reachable, and reaching it gives you a natural moment to check in: is the size right, is the time of day right, do you want to keep going? The mistake is stopping there, or deciding the habit failed because it doesn’t feel automatic yet.

1. Pick a first checkpoint you’re fairly sure you can reach — a week if the habit is new to you, three or four weeks if you’ve done it before.
2. When you reach it, review rather than celebrate and stop. Keep what’s working, shrink what’s hard, and set the next checkpoint further out.
3. Expect the middle stretch to be the hardest. Novelty has worn off and automaticity isn’t there yet. That’s when a plan for missed days matters most.

In Stride: a first goal, then milestones

When you set Stride up, it asks how far you want to take your first streak: 7 days, 21 days or 30 days. Stride marks 21 as the suggested choice. Read that the way this article does — as a first checkpoint that’s ambitious but reachable, not as the day a habit is finished. Until you reach it, Today shows how far along you are.

After the first goal, milestones take over as longer checkpoints: streaks of 7, 30, 100 and 365 days, 100, 500 and 1,000 check-ins in total, and a perfect week — every habit done on every day it was due. They’re on the Stats tab under Milestones, with the date you earned each one and what’s up next.

The short version

• Expect a new habit to take a couple of months, and possibly much longer.
• Judge progress by how automatic it feels, not by whether you’ve hit a magic number.
• Set short checkpoints, and review the habit when you reach each one.