This calculator determine how many calories you need to consume to gain or lose weight. In step 1 of the calorie calculator widget you can input your height, age, gender, weight and your activity level. This information is used to calculate your total daily calorie expenditure. (Calories are a way to measure energy consumed). In step 2 of the calorie calculator widget you can input how much weight you want to gain or lose. Based on this information the calorie widget creates a calorie surplus or a calorie deficit in your diet that will help you achieve your target weight. Depending on how much weight you want to gain or lose you can adjust your calorie intake or your activity level to achieve your desired result.