You will have to exercise to ensure you do not lose muscle mass while you are losing fat mass.

Here is a link to the BMR calculator:
http://www.bmi-calculator.net/bmr-calculat or/

Continue to follow the links to determine your calorie intake needs.

sorry. i do not mean the risk of atrophy. i mean when the body doesn't have enough glycogen, so it goes to the muscle INSTEAD of the fat--any input on that?

It takes 30 grams of protein to burn one pound of fat. So no matter what your basal rate or your BMI, as long as you take in 15-30 grams of protein per day , you can minimize the loss of muscle tissue. On many diets such as Physicians Weight Loss or the Belly Buster Diet, you eat real food and supplement it with protein supplements specifically designed for weight loss. If you are dieting on your own, do not lose more than a pound per week. But, if you join a program where you are monitored and you are on protein, you should lose much faster safely.