BMI Calculator

Body Mass Index (BMI) is a simple numerical measure that uses your height and weight to estimate whether you are underweight, normal weight, overweight, or obese. It was developed in the early 19th century by Belgian mathematician Adolphe Quetelet and remains one of the most widely used screening tools in public health.

BMI is calculated by dividing your weight in kilograms by the square of your height in meters. For imperial units, the formula is (weight in pounds / height in inches squared) multiplied by 703. The resulting number falls into one of several categories defined by the World Health Organization:

• Below 18.5: Underweight
• 18.5 to 24.9: Normal weight
• 25.0 to 29.9: Overweight
• 30.0 and above: Obese

While BMI is a useful starting point, it does not directly measure body fat percentage. Muscular individuals may have a high BMI despite having low body fat, and older adults may have a normal BMI but carry excess fat. For a more complete picture of your health, consider combining BMI with other measurements such as waist circumference, body fat percentage, and blood markers.

Understanding your BMI category can help guide conversations with your healthcare provider about your overall health risks:

Underweight (BMI below 18.5): Being underweight can indicate malnutrition, an eating disorder, or an underlying health condition. It is associated with weakened immune function, osteoporosis, and fertility issues. If your BMI falls in this range, talk to a doctor about possible causes and a plan to reach a healthy weight.

Normal weight (BMI 18.5 to 24.9): A BMI in this range is generally associated with the lowest health risks. Maintaining a normal weight through balanced nutrition and regular physical activity supports cardiovascular health, energy levels, and longevity.

Overweight (BMI 25.0 to 29.9): Carrying extra weight increases the risk of developing type 2 diabetes, high blood pressure, heart disease, and certain cancers. Even modest weight loss of 5 to 10 percent of body weight can significantly improve health markers.

Obese (BMI 30.0 and above): Obesity is a chronic condition that substantially raises the risk of serious health problems including heart disease, stroke, type 2 diabetes, sleep apnea, and joint problems. Medical interventions including dietary changes, increased physical activity, behavioral therapy, medication, or surgery may be recommended depending on the severity.

While BMI is a practical screening tool, it has well-known limitations that are important to keep in mind:

• Does not measure body composition. BMI cannot distinguish between muscle mass and fat mass. Athletes and people with high muscle mass may be classified as overweight or obese despite having low body fat.
• Does not account for fat distribution. Where you carry fat matters. Visceral fat (around the organs in the abdomen) is more dangerous than subcutaneous fat (under the skin). Waist circumference is a better indicator of this risk factor.
• Varies by age, sex, and ethnicity. BMI thresholds were developed using primarily European populations and may not be equally accurate across all ethnic groups. For example, some Asian populations may face elevated health risks at lower BMI values.
• Not suitable for children. BMI is interpreted differently for children and teens using age- and sex-specific percentile charts rather than the fixed categories used for adults.

For a more comprehensive health assessment, consider consulting your doctor about additional tests such as a DEXA scan for body composition, blood lipid panels, and glucose testing.