Body mass index is a number that reflects body weight adjusted for height.
Normal values are 18.5 - 24.9. Values of 25 - 29.9 are considered overweight.
Values of 30 or higher are considered obese.
BMI is not used for muscle builders, long distance athletes, pregnant women, the elderly or young children. This is because BMI does not take into account whether the weight is carried as muscle or fat.
Your basal metabolic rate (BMR) is defined as the rate at which your body uses energy when you are resting in order to keep vital functions going such as breathing. The rate at which your body uses energy to breath and stay warm is an example of your basal metabolic rate. BMR is also known as your body's metabolism.
TDEE, total daily energy expenditure, is the amount of energy in calories you burn per day. TDEE is calculated by factoring in your BMR and your activity level and gives an estimation of how many calories you burn per day when exercise is taken into account.