*This calculator uses a combination of your BMR (Basal Metabolic Rate, or the "base" number of calories needed daily in order to sustain yourself at rest) and the Harris Benedict equation to determine your daily calorie requirements. With the exception of the very muscular (it will under-report calories) and the very obese (it will over report them), it's an accurate tool.
*Weight loss involves many factors. This calculator provides an approximate caloric value to use as a benchmark for acheiving your goals. Attempting to lose more than 1-2 pounds a week through calorie restriction is not practical.