Losing weight is about calories in versus calories out. To lose weight, you need to eat fewer calories than you burn each day through exercise and general living. How much you need to eat each day varies based on your height, weight and activity level. (Find out how many calories you should be eating each day for weight loss by using this formula: [Your weight x 12] – 500 = Your daily calorie goal.) But most people will lose weight on a 1,200-calorie diet, which is also the lowest you really can go calorie-wise each day while still getting all the nutrients you need.