The recommended daily calorie intake is the number of calories a person needs to consume in a day to maintain his or her weight. There are several factors that play into the calculation, including the person's sex, current weight, and level of activity. If the person is trying to gain or lose weight, the suggested number of calories needs to shift to accommodate those goals.
Calculating the recommended daily calorie intake exactly for any given person is very difficult. Everyone has certain variations in his or her resting metabolic rate, or RMR, which is the number of calories your body needs to perform its basic functions, such as breathing and digestion. Also, the amount of daily activity each person gets is a factor, and that can vary from person to person and even from day to day for each person. To get a truly accurate number, a person would need to go into a research lab setting and be monitored by special equipment.
Since going to a research lab is neither convenient nor widely available for most people, there are equations designed to help people calculate a close approximation of their recommended daily calorie intake. Equations such as the Mifflin-St. Jeor take several values, including height, weight, and sex, and use them to make a calculation for RMR. A person would then also have to account for any calories burned during physical activity, which increases the number of calories needed each day. These numbers can give a good rough estimate, though they will probably not be absolutely accurate. There are many online calorie calculators available to help make the process relatively easy.
Another, somewhat simpler but more long-term way to estimate recommended daily calorie intake is to track one's weight and how many calories are being consumed each day. If a person's weight stays steady, then he or she can figure that calorie intake is correct. If weight goes up or down, then calories may need to be adjusted accordingly.
If a person's goal is to lose weight, then recommended daily calorie intake needs to be re-evaluated and lowered. In order to lose fat, calories should be reduced by a moderate amount; extreme calorie reduction will likely trigger a starvation reaction in the body which may detract from weight loss efforts. Dietary changes should be accompanied by an increase in physical activity, which helps burn additional calories and also promotes a higher RMR overall.