If you want to neither lose nor gain weight, this is achieved through maintaining a calorie equilibrium. If the number of calories you consume each day is equal to your body's calorie needs for energy, you will keep a steady weight. Calorie needs can be estimated, but vary from person to person.
The number of calories required to maintain a steady weight of 160 pounds depends on whether you are male or female. A 30-year-old female with a height of 5 ft 8 inches and a somewhat active lifestyle -- defined as light to moderate physical activity two or three times per week -- would require an average of 2,000 calories daily to maintain her weight. A 30-year-old male with the same height and activity level would require 2,300 calories to maintain a weight of 160 pounds.
Your age plays an important part in determining your daily calorie requirements. According to the MayoClinic.com calorie calculator tool, an 18-year-old female with an active lifestyle and a height of 5 ft 5 inches requires 2,250 calories daily to maintain a weight of 160 pounds. At age 80 -- with the same height, weight and activity level -- the same female requires only 1,850 in order to maintain a steady weight.
Because physical exercise burns energy in the form of calories, your daily calorie requirements for weight maintenance will vary according to your general activity level. A 40-year-old male with a height of 6 feet even will require 2,050 calories daily for weight maintenance if he is physically inactive, 2,250 calories if he is somewhat active, 2,450 calories if his lifestyle is active, and 2,900 calories for a very active lifestyle involving daily moderate or vigorous activity.