Age

• Age makes a difference in how many calories you require. Children need energy for growth; adults need energy for maintenance. In a "Good Housekeeping" article, Dr. Madelyn H. Fernstrom, director of the University of Pittsburgh's Weight Management Center, states that your metabolism will slow by 5 percent with each decade of life.
  
  

Gender

• Overall, men's body fat percentage is lower than that of women, and their lean muscle mass percentage is higher. Muscle requires more energy than fat, so the average man will need more calories than the average woman. A woman's required caloric intake increases, however, if she is pregnant or breastfeeding.
  
  

Activity Level

• A person who lives an active lifestyle by engaging in regular, vigorous exercise needs more calories than a person who lives a sedentary lifestyle and performs only day-to-day activities. For optimum health, caloric intake must be balanced with an exercise program appropriate to the person.
  
  

Caloric Requirements

• A 35-year-old man who is 5 feet 9 inches tall would need 1,950 calories per day to maintain a weight of 150 pounds, if he's sedentary. A 45-year-old woman who is 5 feet 2 inches tall would need 1,800 calories per day to maintain a weight of 120 pounds, if she's active. Important guidelines include Body Mass Index (BMI), calculated from height and weight, and the Harris Benedict Equation, which applies activity level to Basal Metabolic Rate (BMR). Please see Resources for a calorie calculator, BMI calculator and the Harris Benedict equation.