How long should you walk to lose weight?

A single step. Every movement requires calories, so, technically, a single step will result in weight loss, and assuming your intake of calories remains constant, you would lose weight in the long-term. Realistically though, a 120 pound person burns about 215 calories an hour walking at moderately fast intensity. A pound of human fat has about 3200 calories, so about 15 hours of walking would burn about a pound of fat- assuming your intake of calories remained constant and all of these calories burned were from fat (not carbohydrates you had eaten, or protein). That sounds a bit depressing for those trying to lose weight quickly- and it is. Higher-intensity exercise such as cycling can burn many more calories per hour- around 600 an hour. More importantly though is what one can realistically continue to maintain over a lifetime. Reducing your exercise level back to a sedentary level while maintaining the same intake of calories will cause you to return to your old weight when you were sedentary. Maintain a small caloric deficit everyday until you reach your goal weight- that is, burn more calories than you consume. When you reach your goal weight, increase your caloric consumption just enough so that your weight stabilizes. The American Heart Association recommends AT LEAST 30-60 minutes of moderate intensity exercise for everybody, everyday, just for good health, more if you want to lose weight. So get moving and remember that exercise is not just a means of dropping weight, it's a means of staying healthy- so get in the habit!