Let's start by looking at how many calories you would need per day just to maintain your weight. Take your current weight and multiply by an "average metabolic factor" to tell you approximately how many calories you burn per day at rest. In our weight loss program, we use a metabolic factor of 11 for women and 12 for men. For example, a 160 lb. woman could theoretically eat: 160 x 11 = 1,760 calories per day to maintain that 160 lb. weight. Note that this does not factor in calories that you might burn through physical activity, so any calories burned through exercise get added to the "calorie budget," so to speak. For example, our 160 lb. woman who burned 300 calories per day with her workout could theoretically eat 2,060 calories per day and maintain her body weight. (1,760 maintenance calories + 300 workout calories burned)
If your goal is to lose weight, take the weight you'd like to be (or your health care provider has recommended) and multiply by the metabolic factor to determine the maintenance calories for your particular goal weight. If our 160 lb. woman wants to weigh 140, for example, we would take the 140 goal weight, multiply by 11 and this would give us a weight loss calorie intake of 1,540 per day. The advantage of this approach is that right from the start you will be eating a diet that will be at the same calorie level you will need to maintain the weight loss once you have reached your goal.
Another approach to weight loss (and here comes more math!) is to look at how much weight you would like to lose, on average, per week and determine how many calories to cut out of your diet to achieve that goal. Let's look at a rate of a one pound loss per week: One pound is equivalent to 3500 calories. To determine how many calories to cut out of your calorie budget per day, divide 3500 by 7 (days of the week); that calculation tells you that you would need to consume 500 calories less each day to lose a pound per week. Note that you could also achieve this goal by burning 500 more calories with physical activity.
An important caveat overall: In our weight loss program, we do not recommend a daily calorie intake below 1200 calories without proper medical supervision.