A very general equation to follow for daily calorie intake is:
Your weight times 18 to gain weight
Your weight times 15 to maintain weight
Your weight times 12 to lose weight
You should never eat less then 1,000 calories per day-this actually causes your metabolism to go into shock and start storing body fat.
One of the best ways to find out exactly how much you need to eat on a daily basis is take a Metabolism Test. Many fitness centers and gyms have a device you breath into for a couple minutes and it measures your RMR (Resting Metobolic Rate). This number accounts for 70% of the daily calories you burn (at rest). Once you know that number you can find out if you really need to eat 12,000 calories per day to compete in your job!