A safe rate of weight loss is ½ -1 pound per week. You'll need to burn an extra 250 calories per day to lose ½ pound per week and 500 calories per day to lose 1 pound per week. A 140-pound person can burn approximately 330 calories by walking for 60 minutes at a pace of 4 miles per hour.. How to Lose 20 Pounds. You'll need to burn an extra 70,000 calories to lose 20 pounds; depending on your starting weight it may take you 20 weeks or more to lose the weight. Set short-term goals and keep food and weight diaries to help you track your progress.