how many fewer calories = losing a pound in weight

The amount of weight you lose can be expressed in a "calorie deficit" that you build up through cutting calories and working out. You need to reach a deficit of 3,500 to lose each pound. That means that if your basal metabolic rate is around 2,000 and you begin eating just 1,400 calories per day, you'll build up a weekly deficit of 4,200 calories, or enough to lose about 1.2 pounds per week. If you also burn about 300 calories per day through exercise, you'll lose a total of closer to two pounds per week. To get an accurate idea of how many calories you're taking in, use an online calorie counter and record everything you eat and drink.

yeah good summary and true, except that the word weight should be swapped with fat. Calorie deficits over time produce fat loss which not necessarily implies a weight loss of the same amount, obviously they are correlated but can proceed at different paces