BMI, or Body Mass Index, provides a straightforward means to assess one's body weight in relation to height, potentially determining one's overall health through the ratio of body weight to height. BMI is calculated using a person's height and weight, and provides an exceedingly brief assessment of body composition along with additional risk factors. BMI is a widely utilized measurement by physicians, fitness professionals, and healthcare organizations around the world for screening individuals to identify those at risk for weight-associated health problems.

Individuals can be grouped into the following four categories: Underweight, Normal Weight, Overweight, and Obesity. These categories provide an indication of an individual's risk of developing health problems associated with low or excessive body fat. Health risks associated with being Underweight can be low nutritional levels, decreased immune response, or loss of bone mass; while there are health risks associated being Overweight and Obese that can include cardiac conditions, elevated blood pressure or developing Type 2 Diabetes Mellitus, Sleep Apnea and developing joint pain.

Even though BMI is a popular tool due to the straightforwardness of its calculations, there are some downsides to it. It does not provide an accurate measurement for body composition in terms of the amount of fat, muscle mass, bone density or how the weight is distributed throughout your body. Therefore, highly-trained athletes will often hav a high BMI despite being very lean. Also, this means that someone who has a 'normal' average BMI can still have a body fat percentage that would be considered extremely high. There are also different factors that determine how you should evaluate your BMI (such as age, gender and ethnicity).

For children and young people, there are different ways of interpreting BMI readings as the percentages of fat change as children develop and grow older. Therefore, in many countries around the world, the health professional will assess a child's BMI using actually the percentage of their age that would equate to their current BMI. Some countries or medical professionals may also have slightly different BMI classification ranges based upon healthy living studies within their own populations.

Although BMI is not perfect, it is still useful as a general indicator of health and can help show when more medical examination, lifestyle changes or improvements in fitness may be needed. A combination of all health measurements (waist size, body fat percentage, diet, exercise activity and total medical history) will provide the best overall assessment of your health status with regard to BMI.