Weight2Weight uses a Current weight, a New weight, an Activity level, Height and Age to calculate the Calories required each day to sustain these weights, and their associated Body Mass Indices (BMI). It also can estimate the weight change after a given number of days, or the number of days needed to reach a target weight for a change in caloric intake. It includes provisions for metric and English units, different daily Calorie requirements for male or female and five activity levels, plus options for three different calculated basal Calories/day/lb estimates and a custom Calories/day/lb.