By reducing "excessive sitting" to less than three hours a day, the U.S. life expectancy could increase by two years, according to a July 2012 study in BMJ Open . Reducing TV time to less than two hours a day would bump it up by 1.4 years. (By comparison, smoking knocks off 2.5 years of life expectancy for men and 1.8 years for women.) The study estimated that the average adult spends 55 percent of his or her day doing something sedentary, but also notes that even high levels of self-reported sitting could be conservative. It's not easy to remember all the time you've spent sitting during the day, since it's not necessarily a domain-specific behavior like watching TV.