20 minutes a day. 30 minutes of exercise 20 minutes a day. How Much Exercise Do You Need? Physical Activity Guidelines School of Public Health Harvard School of Public Health Harvard School of Public Health Studies have shown Harvard says 30 minutes of exercise Harvard School of Public Health exercise Harvard says Harvard School of Public Health 30 minutes of exercise Harvard T. H. Chan School of Public Health Physical activity guidelines: How much exercise do you need? Harvard School of Public Health 20 to 30 minutes Harvard School of Public Health Harvard School of Public Health how steadily recommended 30 minutes of exercise Harvard School of Public Health Harvard T. H. Chan School of Public Health a recommended 2.5 hours of exercise each week standard recommendation