BMI Calculation (Body Mass Index)
Body mass index (BMI) calculation is a useful tool to determine whether a patient falls within an appropriate weight range for their height. It is important to consider other patient characteristics or comorbidities in addition to this parameter.
General Description
BMI calculation is performed to determine whether a patient has an appropriate body weight or falls outside healthy limits for their height. BMI provides information about an individual’s body fat level and allows classification into different categories: underweight, normal weight, overweight, or obesity.
According to the World Health Organization (WHO), BMI calculation is one of the most effective tools for assessing an individual’s health and nutritional status.
When is it indicated?
BMI calculation is recommended during any routine medical check-up to assess the patient’s health status, as well as to determine the presence of malnutrition or obesity that may lead to other conditions, such as infertility, coronary artery disease, or hypertension, among many others.
How is it performed?
BMI is calculated using a general formula developed by Adolphe Quetelet in the 19th century: the patient’s weight in kilograms divided by the square of their height in meters. The result is expressed as a value in kg/m². In children, age-specific BMI is considered according to standardized growth charts.
An adult is considered underweight if BMI is less than 18.5, overweight if it ranges between 25 and 29.9, and obese when BMI exceeds 30.
Risks
BMI calculation does not pose any health risks.
What to expect from a BMI calculation
On the day the data are obtained for BMI calculation, fasting is not required, and usual medication can be taken. This process takes only a few minutes, after which the patient can immediately resume their routine.
To obtain an accurate weight, it is recommended to use a properly calibrated scale and wear minimal clothing. Height should be measured without shoes, standing upright with feet together. Using these data, BMI is calculated. Although patients can apply the formula themselves and consult classification tables, evaluation by a specialist is recommended, as additional health-related factors may be taken into account.
In general, for adults (both men and women), the following ranges are used:
• Underweight: BMI <18.5.
• Normal weight: BMI 18.5–24.9.
• Overweight: BMI 25–29.9.
• Moderate obesity: BMI 30–34.9.
• Severe obesity: BMI 35–39.9.
• Morbid obesity: BMI ≥40.
In pediatrics, percentile curves established by the WHO are used, stratified by age and sex.
Results are obtained during the same consultation; therefore, the specialist will typically establish, when necessary, a treatment plan or dietary recommendations to achieve an appropriate BMI.
Specialties in which BMI calculation is requested
BMI calculation is applied across multiple medical specialties, primarily in Family and community medicine, Endocrinology and Nutrition, Assisted reproduction, Gynecology and Obstetrics, Cardiology, and Plastic, aesthetic and reconstructive surgery.
How to prepare
No prior preparation is required to obtain the data needed for BMI calculation.
