If It Takes 21 Days to Change a Habit, Why Do So Many People Still Break Them?

Building habits takes time, repetition and support.

"Just stick with it for 21 days and it’ll become a habit!"

It’s a phrase you’ve probably heard before – maybe even tried to follow. On the surface, it sounds motivating. Just three weeks of early morning runs, gym sessions, or healthy eating and your new lifestyle is locked in… right?

But here’s the problem: it’s not that simple. In fact, this idea might be one of the reasons people fall back into old habits – just when they thought they were making progress.

The 21-Day Myth: Where It Came From

The belief that habits take 21 days to form can be traced back to Dr Maxwell Maltz, a plastic surgeon in the 1950s. He noticed that his patients typically needed about three weeks to adjust to a change in appearance. Later, in his book Psycho-Cybernetics, he wrote that it took “a minimum of 21 days” to adjust to a new situation or habit.

Over time, that subtle phrase – a minimum of – got dropped. Self-help books and social media posts boiled it down to a catchy line: “21 days to a new you!” It spread because it sounded doable.

But it’s not grounded in real science.

What the Research Actually Shows

A much more detailed study from University College London (Lally et al., 2009) followed 96 people over 12 weeks as they tried to build simple new habits – like eating more fruit or going for a daily walk.

The results? On average, it took 66 days for a behaviour to become automatic. Some took far longer – up to 254 days – depending on the complexity of the habit and the person’s lifestyle.

That’s over two months. Not three weeks.

This research made one thing clear: building habits takes time, repetition, and support – not a countdown.

Why Do Habits Still Break After 21 Days?

Even if someone has made it through three solid weeks of workouts, better food choices, or regular walking, old habits can creep back in. Why?

Because short-term effort doesn’t guarantee long-term change. Here are a few reasons why habits don’t always stick:

• The pace is too intense – Going from zero to five workouts a week might feel productive, but often leads to burnout.

• Nothing else changes – You’re trying to eat healthier, but your fridge and routine haven’t been set up to support that change.

• Motivation fizzles out – Motivation gets you started, but systems and structure are what keep you going.

• You haven’t become “that person” yet – The behaviour hasn’t shifted your identity. If you still don’t see yourself as someone who trains regularly, it won’t last.

What Actually Helps Habits Stick?

Habits are more likely to take hold when the friction is low and the environment works with you, not against you. It’s about making the behaviour easy and obvious.

Some practical ways to do this include:

• Lay your gym kit out the night before – reduces morning friction

• Schedule your workouts like meetings – you’re more likely to honour them

• Start small and stay consistent – don’t go all in, go all steady

• Link new habits to existing ones – for example, stretch while the kettle boils

These simple changes aren’t gimmicks – they create the structure that supports consistency, even when motivation is low.

Real Coaching. Real Change.

Here’s how this looks in real life.

Client Case Study: Emma, 38, solicitor, NW London

Goal: Rebuild confidence with exercise after 10+ years away

“I’d tried Couch to 5K, bootcamps, detoxes – but nothing stuck. Coaching with Andrew helped me build habits I could actually keep. We started small, focused on what was realistic, and I didn’t feel like I had to be perfect. Now I train twice a week, I’m stronger, my sleep is better, and exercise feels normal – not forced.”

Emma’s progress didn’t come from pushing harder. It came from a structured, sustainable approach built around her real life – with the right support and consistency.

One-to-One Coaching That Builds Lasting Habits

As a health and fitness coach based in NW London, I work with people who are tired of starting over. My focus isn’t just on getting you active – it’s on helping you stay active. That means:

✅ Tailored training that fits around your life

✅ Habit coaching based on behavioural science

✅ Support and accountability without pressure or perfection

✅ A focus on long-term change, not short bursts of effort

Whether you're just starting out or returning after a break, I’ll help you build fitness habits that genuinely last – not just for 21 days, but for life.

Ready to Stop Starting Over?

If you’re done with quick fixes and want a proper plan to feel stronger, healthier, and more in control – I’d love to help.

📍 One-to-one personal training and coaching in North West London 📩 Message me for a free consultation call – let’s chat about your goals