This calculator is just for adult females. There's also a men's calculator. Be sure to speak with your health care provider before starting on any weight loss diet.
Sources:
American Dietetic Association. "In non-obese individuals, what is the prediction accuracy and maximum overestimation and underestimation errors compared to measured resting metabolic rate when using the Harris-Benedict formula?" ADA Evidence Analysis Library. Published March 2005.
"Food Intake Patterns." U.S. Department of Agriculture Center for Nutrition Policy and Promotion. Accessed April 2005.