Work out habit formation days instantly with clear inputs, formula shown and shareable results.
Automaticity is treated as a repetition count rather than a fixed number of days, and the time required is that count divided by the repetitions you actually complete each week. The oft-quoted 21 days is a myth; the research finds a wide range centred nearer 66 days, and it is repetitions rather than calendar time that drive the change.
Time to automaticity
weeks = repetitions needed / (planned repetitions per week x (1 - miss rate))
weeks = repetitions needed / (planned repetitions per week x (1 - miss rate)). Automaticity is treated as a repetition count rather than a fixed number of days, and the time required is that count divided by the repetitions you actually complete each week.
The oft-quoted 21 days is a myth; the research finds a wide range centred nearer 66 days, and it is repetitions rather than calendar time that drive the change.
Enter repetitions per week, difficulty of the habit, share of planned repetitions you miss. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.