Building Habits That Stick
Why 21 days is a myth and what the research really says.
The 66-day finding
A University College London study found habits took 66 days on average to feel automatic, ranging from 18 to 254 days.
Make it easy
Start tiny, link the habit to an existing routine and put cues where you will see them.
Missing a day
One missed day did not derail habit formation. Resume the next day without guilt.
Try it: Habit Formation Calculator
Example with sample values. Open the full calculator →
Days since start21
Consistency85.7 %
Estimated automaticity47.4 %
Research found habits took 66 days on average to become automatic, with a range of 18 to 254 days. The curve shown is an illustration, and missing a day rarely matters.
Educational content only. This article does not replace advice from a qualified health professional. Medical disclaimer.