While any amount of exercise is an improvement over none at all, if you're already in decent shape, exercising for just two days a week will not get you much additional benefit. Here's what he told us when we asked him how often you should exercise: A minimum of three days per week, for a structured exercise program. Technically, you should do something every day, and by something I mean physical activity — just move. Because we're finding more and more that the act of sitting counteracts any of the activity you do.