Module 10 · The science in depth · Supported by multiple studies

What the research says about “how long”

Reading the studies behind the numbers — and the huge individual variation.

7 min read · Level: Advanced · Free — no account needed to read

The problem it solves

What do the studies behind “how long it takes” really show?

The concept

The best-known study followed volunteers repeating one simple behaviour daily in the same context for twelve weeks. For those whose data fitted the model, the time to reach near their own plateau of automaticity had a median of 66 days — and ranged from 18 to 254.

A 2024 review pooled 20 studies and found medians of around two months, averages longer, and individual times from a few days to most of a year; morning practices and self-chosen habits tended to be stronger. A machine-learning study found hand-washing at work became predictable in weeks, and gym-going in months.

The consistent message is individual variation: the behaviour, the person, the context and the measure all change the answer.

Why it matters

This is the evidence behind “there is no universal habit-formation deadline” — and a model of how to read any habit number you see.

Supported by multiple studies: Many studies, often pooled in reviews or meta-analyses, point the same way. It still works better for some people and situations than others.

See it happen

Two friends start the same stretching habit on the same day. One finds it automatic in weeks; the other still has to think about it after three months.

The ordinary first approach

The second friend must be doing something wrong.

With the idea

The research predicts exactly this spread; the second friend checks their cue and keeps going.

What changed

Variation became expected rather than alarming.

Easy to get wrong

• Quoting a median as if it applied to everyone.
• Ignoring that many participants’ data didn’t fit the model.
• Comparing your pace with someone else’s habit.

Try it now: Read the fine print

1. Pick one claim about how long habits take.
2. Ask: what behaviour, what measure, how many people, how much variation?
3. Rewrite the claim with its limits included.

Apply it to one of your habits

For one of your habits, is it more like hand-washing (simple, frequent) or gym-going (complex, effortful)?

Reflect

• How does knowing about the range change your expectations?

Go deeper — evidence & sources

• Lally, van Jaarsveld, Potts & Wardle (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology. doi:10.1002/ejsp.674
• Singh, Murphy, Maher & Smith (2024). Time to Form a Habit: A Systematic Review and Meta-Analysis of Health Behaviour Habit Formation and Its Determinants. Healthcare. doi:10.3390/healthcare12232488
• Buyalskaya, Ho, Milkman, Li, Duckworth & Camerer (2023). What can machine learning teach us about habit formation? Evidence from exercise and hygiene. Proceedings of the National Academy of Sciences. doi:10.1073/pnas.2216115120
• Keller, Kwasnicka, Klaiber, Sichert, Lally & Fleig (2021). Habit formation following routine-based versus time-based cue planning: A randomized controlled trial. British Journal of Health Psychology. doi:10.1111/bjhp.12504