How To Build Better Habits With the 21/90 Rule

Building good habits is the key to a better life.

If you go to the gym each morning, you cannot help but get fit. If you train yourself to call 5 new clients each day, your business will prosper.

Yet the tricky part is not introducing the habit, but sticking with it.

This is where the 21/90 rule comes in. By not breaking the chain for 111 days, the new behavor will eventually become effortless.

Read on to learn how exactly the 21/90 rule works and what you can do to get the most out of it.

Definition: What Is the 21/90 Rule?

The 21/90 rule states that it takes 21 days to form a new habit and 90 days to create a permanent lifestyle change.

Put differently — 3 weeks of habit formation, 3 months of habit solidification.

Let’s say you commit to doing 100 air squats a day.

In the beginning, that will require significant willpower. After about three weeks, though, the new behavior should have become a habit. It will now be relatively easier to do.

If you continue for another 90 days, the habit will become ingrained so deeply, it is now part of your lifestyle. You will do your squats like you brush your teeth every day.

How It Works

The underlying idea of the 21/90 rule — give a new habit enough time, and it will become automated.

Once that automation has taken place, it is much easier to add another habit, since you have willpower available again.

In this sequential manner, you can build one healthy habit after another, without experiencing mental overload. Yet over the time, these small habits will yield big results, similar to how compound interest in finance works.

The 21/90 rule ensures the smoothness of that process. By subscribing a phase of 21 + 90 days, it paces us when we want to rush the process (which always backfires).

People do not decide their futures, they decide their habits and their habits decide their futures.

F.M. Alexander

Who Made the 21/90 Rule?

The idea that it takes 21 days to form a habit is falsely attributed to Dr. Maxwell Maltz, an American cosmetic surgeon and author. His most well-known book, “Psycho-Cybergenetics,” was published in 1960. Here he made the following observation regarding his patients:

It usually requires a minimum of about 21 days to effect any perceptible change in a mental image. Following plastic surgery it takes about 21 days for the average patient to get used to his new face. When an arm or leg is amputated the “phantom limb” persists for about 21 days. People must live in a new house for about three weeks before it begins to “seem like home.” These, and many other commonly observed phenomena tend to show that it requires a minimum of about 21 days for an old mental image to dissolve and a new one to jell.

Note that Maltz was talking about self-image, the subject of his book, not habit formation.

Also note that he mentioned a “minimum of about 21 days” — not exactly 21 days.

Yet, the formula of “21 days to form a new habit” caught on, and kept being recited by several famous self-authors throughout the following decades.

That explains the 21-days part of the 21/90 rule. But it is not clear where the “90 days” part comes from.

My guess is that the whole concept started out as an internet self-help meme. Someone came up with a catchy visual, and it got shared. The numbers seem to support that theory — only as late as 2016 was there any search volume for the term “21 90 rule” in Google.

Is the 21/90 Rule True?

Sort of.

There are various studies on habit formation. One of the better known, a study done at University College London in 2009, concluded that on average it takes 66 days before a habit starts to feel automatic.

But there was a wide range. Some of the 96 participants reported that it took them as little as 18 days to automate a habit, while others took as long as an extrapolated 254 days (the study was only 12 weeks).

So if you look at the 111 days (21 + 90 days) that the 21/90 rule prescribes, that guideline seems reasonable. If anything, it errs on the safe side. Which is a good thing, as most people don’t give habits enough time to “gel.”

Also take into account that the number of days will always vary depending on the difficulty of the task. Drinking a glass of water in the morning will be easier to automate than doing a hard workout each day.

Does It Matter?

Personally, I think it’s a bit silly to get hung up on the exact number of days needed to form a habit.

The 21/90 rule is a good guess, definitely a better one than the classic “it only takes 21 days.” It implies that habit formation requires more patience than commonly thought.

That alone is to be encouraged.

At the same time, by prescribing 3 weeks + 3 months, a rather long time frame suddenly seems doable. That helps with compliance.

Most importantly, the 21/90 rule gives us something to shoot for. Because it’s so straightforward, it entices us to take action.

All of that makes the 21/90 rule a great method for habit formation.

How To Get the Most Out of the 21/90 Rule

Pay attention to the following 10 best practices, to maximize your results with the 21/90 rule.

1. Set Your Goal

The first step is to decide what new daily habit you want to implement. Here are a few ideas:

Health related habits:

  • Eat a serving of vegetables with each meal
  • Eat a serving of high-quality protein with each meal
  • Eat a paleo diet
  • Walk 10,000 steps
  • Do 50 push-ups
  • Stretch for 10 minutes
  • Get at least 8 hours of sleep
  • Go to bed at the same time

Career/finance related habits:

  • Spend 30 minutes learning a job-related skill, like programming
  • Spend 30 minutes building a side hustle
  • Make three cold calls
  • Save amount X every month

Self-development related habits:

  • Practice an instrument for 30 minutes
  • Practice to draw for 15 minutes
  • Practice a new language for 20 minutes
  • Read 10 pages of a challenging book
  • Meditate for 5 minutes
  • Journal for 10 minutes
  • Write down 3 things you are grateful for

Relationship related habits:

  • Show someone your appreciation
  • Introduce somebody to someone else
  • Talk to a stranger

Instead of adding a new habit, you could also decide to drop a bad habit. Here are few examples:

  • Stop eating junk food
  • Stop smoking
  • Stop drinking at night
  • Stop watching binge-watching Netflix
  • Stop blaming others
  • Stop telling lies in conversations

I recommend starting with a smaller goal for your first cycle of the 21/90 rule. Once you have proven to yourself that you can go through with, tackle a slightly more challenging habit.

Discipline is choosing between what you want now and what you want most.

Abraham Lincoln

2. Choose One Thing

When you are excited about improving yourself, it is tempting to keep adding habits. “I will work out every day, I’ll call five new clients, and at night, l’ll practice Spanish for an hour.”

And on your best days, you will indeed be able to do all of these things.

But on many other days, you will be busy and/or tired. And then you will break the chain, because you committed to too many new behaviors at once.

Ideally, you should never break the chain. Remember — we are trying to do this for 21 + 90 days in a row.

Choose only one thing to implement. But keep doing that, even on bad days. This way, you will eventually reap the benefits of automation.

Pace yourself and you will succeed. Bite off more than you can chew, and you will keep failing.

He who is everywhere is nowhere.


3. Start Tiny

Whatever one habit you choose, make sure it is easy to do in the beginning.

Let’s say you want to practice the guitar every day. Instead of right away practicing for an hour each night, start with a mere 10 minutes.

This way, you will easily stick with the new habit during the first few weeks. That will make you feel good, and act as positive reinforcement for the new behavior.

Once these 10 minutes start to fly by, add another 5 or 10 minutes to your daily session.

Again, the idea is to not overtax yourself. Do not get carried away by your initial enthusiasm. Plan for the bad days, when you feel beat up. You must still be able to continue the chain on those days.

4. Write It Down

When you have chosen the one habit you want to implement, write it down. This way, you make an official agreement with yourself what you are committing to.

Be as specific as possible. “Workout every day” is not very specific. “Do 3 sets of air squats to failure every day, first thing when I get home from work” is much more specific.

Put your written agreement up in a visible place. Then read it to yourself aloud first thing in the morning to prime yourself for the day.

5. Time Block

To really make sure your new habits gets done, it’s best to time block it. Reserve a certain slot on your calendar every day to make sure it gets done.

For example, if you want to call 3 new prospective clients each day, you might block an hour before lunch for that, from 11 am to 12 pm.

In addition, I also like to set a daily alarm on my smartphone. This way I don’t forget about the 21/90 rule, even on a very hectic day.

This date with yourself should be sacrosanct. Short of someone dying, nothing is allowed to interrupt you. Also, no social media or other distractions.

6. Practice Accountability

Studies have consistently shown that we are more likely to go through with a new behavior if we have an accountability partner. This could be your workout buddy, a paid coach that checks in on you once a day, or a virtual accountability service like stickK.

You can also increase accountability by telling the people you surround yourself with about your new behavior. Now is there is more pressure on you to go through with it. Better yet, start a blog or a vlog documenting your daily progress and share this with your network.

Eventually, when the 21/90 rule starts to kick in, the accountability element won’t be necessary anymore. Now the new behavior has become part of yourself. But to get to that point, you need to practice accountability first.

7. Find Outside Motivation

Especially during the first few weeks of the 21/90 rule, it can be helpful to inject some outside motivation into the process.

For example, when you are trying to lose body fat, it can be encouraging to watch videos of people who already did so.

This will give you a quick rush of motivation. It will get you going again at moments when you are running out of steam.

Three words of caution though.

First, don’t mix up the outside motivation with the actual doing. For you to get lean, it’s not enough to binge-watch fitness gurus on YouTube. You must still do the work.

Second — speaking of gurus — be aware that many people make a living from motivational content. Try to watch real people, not salesmen.

Third, realize that like any induced high, motivation eventually wears off. That’s not bad in itself, you just need to plan for it.

Of course motivation is not permanent. But then, neither is bathing; but it is something you should do on a regular basis.

Zig Ziglar

8. Reward Yourself

You can reinforce a new habit by connecting it to a reward.

Let’s say you are trying to learn how to program, which is a demandig task.

To reward yourself, you could make an agreement. Every time you go through with your daily 1-hour programming session, you get to eat some dark chocolate.

Be careful not to install new bad habits through the backdoor. Some dark chocolate is fine, a box of Krispy Kreme Donuts not so much.

9. Punish Yourself

You can also reinforce a new habit by connecting it to a punishment.

Let’s stay with our programming example. But this time, when you don’t stick to the habit, you have to pay amount X to someone you don’t like.

Some people might even rip up or burn a $20 bill, each time they fail (which is illegal, so I am not suggesting it).

It works like a charm, though. As I can attest, it is almost physically painful to waste money in that way.

The tricky part with self-punishment is how to avoid excuses. For that, you usually need to involve another person to act as a referee.

For example, you could give $600 to someone you trust for a month in advance ($20 x 30). They would then give you back $20 each day you stick with your new habit.

10. Track Your Progress

Always track your progress with your chosen habit. What gets monitored, gets managed.

It could be as easy as putting up a calendar print-out for the current month. For every day you stick with your chosen habit, you put a big red cross on there. Make sure to mark both the 21-day milestone and the succeeding 90-day milestone.

If you prefer technology, you could note down your progress in a Google sheet or use one of the many free tracking apps. If you opted for blogging about your progress, you could include your tracking here, for all the world to see.

It doesn’t matter what tool you use, as long as you are diligent about the tracking. Never try to wing it in the beginning. That only works once the habit — via the 21/90 rule — has become a permanent lifestyle change.


Here are some of the most frequently asked questions in regards to the 21/90 rule.

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