To figure out how many calories you should have, first start with where you are. In other words, figure out how many calories it takes to maintain your present size and then reduce from there. You can go about this in many ways. Most people simply choose an arbitrary number like 1200 calories and that's what they eat, but in nearly every case that's not nearly enough calories to ensure adequate nutrition, not to mention the deprivation that sets up.
While losing weight and to this day, I eat over 2000 calories a day on average and I've maintained a good weight for my height for over 17 years. Remember, your body requires calories to maintain itself.
Basic Calorie Requirements Calculation Based on Activity Level:
Sedentary : 13 X Weight = Avg. cal/day
Sedentary is not exercising at all
Moderately Active: 16 X Weight = Avg. cal/day
Moderately Active is exercising approximately 3-4 times per week
Very Active: 19 X Weight = Avg. cal/day
Very Active is 5-7 strenuous exercise sessions per week.
If you weigh over 200 pound now, and you'd like to weigh closer to 150, here is a calculation you could use to get started: Assuming you are going to be adding enough exercise to quality as Moderately Active, we'll use 16 as our modifier:
150 pounds X 16 calories per pound = 2400 calories
Less 500 (Using the common 500 calories per day reduction) gives us a total of 1900 average calories per day