Calculate your Body Mass Index and see where you fall on the healthy weight spectrum.
Body Mass Index (BMI) is a screening tool that uses your height and weight to estimate whether you fall into an underweight, normal weight, overweight, or obese category. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and adopted by the World Health Organization as a population-level health indicator.
A BMI between 18.5 and 24.9 is considered normal weight by the WHO and CDC. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is obese. These thresholds were established based on large population studies linking BMI ranges to health outcomes including cardiovascular disease, Type 2 diabetes, and all-cause mortality.
Enter your weight and height using either imperial (pounds and feet/inches) or metric (kilograms and centimeters) units. The calculator instantly shows your BMI number, the WHO category you fall into, and a visual indicator of where you sit on the BMI spectrum. You can toggle between unit systems without losing your inputs.
The standard BMI categories used worldwide are based on WHO classifications. Underweight (below 18.5) is associated with nutrient deficiencies, weakened immune function, and bone loss. Normal weight (18.5-24.9) is associated with the lowest overall health risk. Overweight (25-29.9) carries increased risk for hypertension, high cholesterol, and Type 2 diabetes. Obese Class I (30-34.9), Class II (35-39.9), and Class III (40+) carry progressively higher risks for cardiovascular disease, sleep apnea, certain cancers, and reduced life expectancy.
BMI is a useful screening tool but has well-documented limitations. It does not distinguish between muscle mass and fat mass, which means muscular athletes often register as "overweight" despite having low body fat. It does not account for body fat distribution, and visceral fat (around the organs) is far more dangerous than subcutaneous fat (under the skin). BMI also does not account for age, sex, or ethnicity, all of which affect the relationship between BMI and health outcomes. The waist-to-hip ratio and body fat percentage are often better indicators of metabolic health. You can measure your body fat with the Body Fat Calculator and your waist-to-hip ratio with the Waist-to-Hip Ratio Calculator.
For adults over 20, the same BMI thresholds apply regardless of age or sex. However, research shows that health risks associated with a given BMI vary by demographic. Older adults may have a slightly higher "optimal" BMI (23-27) because moderate weight provides a protective buffer during illness. Women typically have higher body fat percentages than men at the same BMI. And Asian populations tend to have higher body fat percentages and greater metabolic risk at lower BMIs, which is why some countries use modified thresholds (overweight at 23, obese at 27.5).
BMI for children and teens (ages 2-19) is interpreted differently than for adults. Instead of fixed thresholds, children's BMI is compared to growth charts that account for age and sex, producing a percentile. Below the 5th percentile is underweight, 5th to 84th is healthy weight, 85th to 94th is overweight, and 95th percentile or above is obese. This calculator is designed for adults. For children, consult your pediatrician or use a CDC growth chart calculator.
If your BMI is in the normal range, continue maintaining a healthy diet and regular physical activity. If your BMI is in the overweight or obese range, the most impactful steps are increasing physical activity and making sustainable dietary changes. Even modest weight loss of 5-10% of body weight can significantly reduce risk factors for diabetes and heart disease. If your BMI is underweight, focus on nutrient-dense calorie increases and consult a healthcare provider to rule out underlying conditions. Use the Calorie Calculator to find your daily calorie target based on your goal.