It is recommended by the U.S. Surgeon General that everyone needs 30 minutes of physical activity a day. This is intended for people who want to maintain the most basic level of fitness — but not for people who want to lose weight.
In a week, 30 minutes a day works out to an expenditure of about 1,000 calories, which is fine if a person is looking to maintain their current weight. For those that want weight loss, be prepared to do a bit more work.
The World Health Organization recommends 60 minutes at a time as a starting point for individuals starting on a weight loss program. This is ideal to get the most out of workouts and to see significant results. These 60-minute workout sessions should always include a 5-minute warm-up, followed by 50 minutes of primary cardio or strength-training exercises, followed by at least 5 minutes of cooling down and stretching.
Of course, putting in more time will get you more results — but there's a limit. Excessive intense physical activity releases stress hormones, such as cortisol, into the body. This can actually inhibit weight loss, causing your body to react by storing fat and retaining water out of self-protection. So, to reach your weight loss goal, it is recommend to limit intense exercise to no more than two hours a session.