If you weigh 166 pounds and you consume 1200 calories a day how much will you weigh in a month?

No, you would probably only gain 1 lb, at most, that's how much a normal person is suppost to eat anyway. Answer: Weight gain is not a function of present weight or even food intake. To give any estiamate you would need an indication of metabolic rates, caloric output, lifestyle, average temperature of the environment, general health, specific health concerns (e.g. diabetic) and several other factors.