How to Calculate Calories Needed to Gain Weight

Being underweight is just as bad for your health as being overweight. According to the Better Health Channel website, having a body mass index (BMI) below 20 puts you at an increased risk of respiratory disease, cancer, osteoporosis, digestive disease and bone fractures. Your BMI is a number that reflects how much body fat you have. BMI is calculated by dividing your weight in pounds by your height in inches squared and multiplying the result by 703. Whether you want to gain weight for health reasons, or to increase your muscle tissue, you'll have to take in more calories than you expend, to do so.

Instructions

• 1

  Multiply your weight by 11 to get the amount of calories you can consume on a daily basis to maintain your current weight. For instance, if your current weight is 150 pounds, your calculation would be 150 x 11 = 1,650 calories.

• 2

  Know the difference between a slow, moderate and fast metabolism, because you'll have to factor in your metabolic rate. For example, if you gain weight very easily and have a hard time losing weight, you likely have a slow metabolism. If you gain weight when you want to and have no trouble losing weight, then you have a moderate metabolism. If you stay skinny regardless of your caloric intake, or if gaining weight is difficult for you, you likely have a fast metabolism.

• 3

  Find your metabolic factor based on your age and metabolic rate. Use a 30 percent metabolic factor if you're under 30 years of age and have a slow metabolism; use 40 percent if your metabolism is moderate and 50 percent for a fast metabolism.

  Use a metabolic factor of 25 percent if you're between 30 to 40 years of age and have a slow metabolism; use 35 percent for a moderate metabolism and 45 percent for a fast metabolism.

  Use 20 percent as your metabolic factor if you're over 40 years of age and have a slow metabolism; use 30 percent if your metabolism is moderate and 40 percent if it's fast.

• 4

  Take your daily calorie allowance and multiply it by your metabolic factor. For instance, if you're under 30 and have a moderate metabolism, you would multiply 1,650 by 40 percent, which is 660. Add 1,650 and 660 to get 2,310, which is the number of calories you must eat to maintain your current weight, with your current physical activity factored in.

• 5

  Add 500 calories to the total calories you can consume to find out how many calories you have to consume daily to gain weight. The calculation would be as follows: 500 plus 2310 equals 2,810 calories per day. According to The Diet Channel website, you can gain weight healthily by adding 500 calories per day. They suggest that if you don't gain weight after three weeks, you should increase this number to 700 calories per day.