Calorie Intake for Losing Fat and Gaining Muscle

I must admit that I am having a hard time trying to determing what the correct caloric intake should be as a person trying to lose fat and gain lean weight (muscle). I am currently a 27 year old male at 5'11 and 180 pounds. I want to gain 10-15 pounds of lean mass over the next year and lose about the same in fat. I believe my gym assessment suggested I intake 2400 calories a day. However, if I am doing cardio and burning 400-600 calories a day for example, will all those extra calories lost degrade my muscle development? My basic question is this....when trying to gain muscle and lose fat at the same time, should you still be attempting to go under your normal daily calorie instake to lose weight?

Thanks for any help you guys can suggest