Give a new habit ten weeks

"Twenty-one days" is invented. In the best-known careful study, people picked a daily habit and logged how automatic it felt. The middle of the range was about sixty-six days. The spread was three weeks to most of a year, depending on the person and the habit. Missing a single day made no real difference. Evidence: solid

So a habit that still feels like effort at week four isn't failing. It's on schedule. Ten weeks is a fair trial; three isn't. Evidence: decent

Small and daily formed fastest. The study's quickest habits were things like a glass of water after breakfast; exercise took longest. Nobody tested weekly. Evidence: decent