Forever!  “Experts” have written that it takes 21 days, 30 days, 45 days, 60 days, six months, one year, two years, and even ten years to successfully extinguish an old behavior, but in reality, there is no magic number of days that you need to reach to make a new behavior stick.   Another reality is that, during times of stress, there is a strong inclination is to slip back into an old behavior, and so we must constantly work to maintain change by controlling our environment, renewing our commitment, and taking credit for our accomplishments.  Read about behavior change at About.com.