This App is based on the Body Weight Simulator (bwsimulator.niddk.nih.gov) developed by Kevin Hall, Carson Chow and collaborators. The App predicts the body weight time course given specified changes in diet and physical activity or predicts changes in diet necessary to achieve a weight goal. The predictions are based on a validated mathematical model of human metabolism as described in Hall et al., The Lancet. 378:826-37(2011).