Ever wondered how long does it take to break a habit? Scientists and leading psychology research suggest that it takes us around 21 days to break or form a new habit. This means doing a good thing (eating clean, exercising daily) can become your habit if done 21 days in a row. And Bestselling Book “Power of Habit by Charles Duhigg” suggests that an old bad habit cannot be extinguished in a day, but can only be replaced with a new good habit in 21 days period. So if you want to Quit Smoking?