by Charles O. Frazier, MD, FAAFP
1/26/2026

 

How do you define "habit"? I think many of us would define a habit as something we do frequently or customarily, or, perhaps from a negative connotation, something we get "hooked on," such as nicotine or other "habit-forming" substances.

 

But in scientific terms, a habit is a behavior that is prompted automatically by situational cues, as a result of learned cue-behavior connections (Gardner 2015). A good way to think of it is a cue leads to a behavior leads to some sort of reinforcement. Cue - behavior - reinforcement. Over time, the repetition strenghthens the cue-behavior link, and the behavior becomes more automatic. (Gardner 2012)

 

Early on, most behaviors take some effort because they require attention, decisions, and control. With repetition in a stable context, the brain starts to "predict" what comes next and retrieves the behavior with less deliberation. That is why where and when you do something often matters as much as what you do -- consistent cues create the structure for automation (Gardner 2012).

 

And yet, the behavior doesn't necessarily get consistently more automatic over time. One of the most cited real-world studies of habit formation followed people who chose a simple daily behavior (eating, drinking, or activity) and repeated it in the same context for 12 weeks, while tracking "automaticity" day by day. The pattern was not linear: automaticity rose quickly early on, then slowed and leveled off as it approached a plateau (Lally et al., 2010).

 

How long does it take to create a habit? There isn't a consistent answer, because the time it takes depends on the cues, the behaviors, and the individual. In Lally's study, the estimated time to reach about 95% of maximum automaticity had a median of 66 days, but the times varied widely --  roughly 18 to 254 days, depending on the person and the behavior (Lally 2010).

 

A more recent systematic review and meta-analysis focused on health behaviors -- including physical activity, flossing, healthier diet patterns, drinking water, vitamins, and others -- and similarly emphasized both a typical "two-month" signal and very large individual variability. In that review, studies that reported habit-formation times found median values around 59 - 66 days, while mean values were longer, with reported ranges spanning 4 to 335 days (Singh 2024).

The practical takeaway is not "it takes 66 days," but rather: expect meaningful momentum in about 2 months for many simple habits, and plan for several months for more complex ones (Lally 2010; Singh 2024).

If that's the case, then you may wonder why I suggest adopting a new habit in RENEWL every tspan class="auto-style1">wo weeks. It's because I wanted the behavior changes to happen more frequently, and I wanted to offset our metabolism's tendency to counteract weight loss as we seek it over time. Also, remember that I said that automaticity rose quickly at first, but then leveled off over time? I also wanted to keep it interesting over time.

The result is that you quickly develop these habits so that by the end of approximately 5 months, you could be becoming very used to all of these evidence-based weight loss steps.

 

References
Gardner B. A review and analysis of the use of 'habit' in understanding, predicting and influencing health-related behaviour. Health Psychol Rev. 2015;9(3):277-95.

 

Gardner B, Lally P, Wardle J. Making health habitual: the psychology of 'habit-formation' and general practice. Br J Gen Pract. 2012 Dec;62(605):664-6.

 

LLally, P., van Jaarsveld, C. H. M., Potts, H. W. W., & Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998-1009.

 Singh B, Murphy A, Maher C, Smith AE. Time to Form a Habit: A Systematic Review and Meta-Analysis of Health Behaviour Habit Formation and Its Determinants. Healthcare (Basel). 2024 Dec 9;12(23):2488.