BMI Calculator
Calculate your Body Mass Index
How BMI is calculated
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by your height in meters squared. The formula is: BMI = weight (kg) / height (m)². Developed in the early 19th century by Adolphe Quetelet, BMI was adopted by the World Health Organization as a standard population-level screening tool for weight classification. It provides a quick, accessible way to assess whether your weight falls within a range associated with lower health risks. However, BMI has well-documented limitations. It does not distinguish between fat mass and lean mass, meaning muscular individuals may be classified as overweight despite having low body fat. It also does not account for bone density, age-related muscle loss, or differences in fat distribution. The National Institutes of Health recommend using BMI alongside other measurements such as waist circumference and body composition analysis for a more complete picture of health. BMI should be used as a starting point for conversation with your healthcare provider — not as a standalone diagnosis.
What your result means
According to the World Health Organization, a BMI between 18.5 and 24.9 is classified as normal weight and is associated with the lowest risk of weight-related health complications. A BMI below 18.5 indicates underweight, which can signal nutritional deficiencies or underlying medical conditions. A BMI between 25.0 and 29.9 falls in the overweight range, and a BMI of 30.0 or above is classified as obese — a category linked to increased risk of type 2 diabetes, cardiovascular disease, and certain cancers. It is important to understand that BMI does not tell the full story. A well-trained athlete may register a BMI above 25 due to muscle mass, while an older adult with a normal BMI may carry excess visceral fat. Ethnicity also plays a role — research from the NIH shows that health risks may begin at lower BMI thresholds in some populations. For a comprehensive assessment, discuss your result with a healthcare professional who can evaluate additional factors like body composition, blood pressure, and metabolic health.
Frequently Asked Questions
Is BMI accurate for everyone?
No, BMI does not account for muscle mass, age, sex, or body composition. It is a population-level screening tool, not an individual diagnosis. Athletes with high muscle mass may be classified as overweight despite having low body fat, and older adults who have lost muscle may appear to have a normal BMI while carrying excess fat. The WHO recommends combining BMI with waist circumference and other health markers for a more accurate assessment.
What is a healthy BMI?
A BMI between 18.5 and 24.9 is considered normal weight according to the World Health Organization (WHO). However, the optimal BMI varies from person to person depending on age, sex, muscle mass, and ethnicity. Some research suggests that a BMI around 22 to 23 is associated with the lowest overall mortality risk, but individual health markers matter more than any single number.
Can children use this calculator?
No, this calculator is designed for adults aged 18 and older. BMI for children and adolescents is calculated differently using age- and sex-specific growth charts, often referred to as BMI-for-age percentiles. The CDC and WHO provide separate pediatric BMI charts because children's body composition changes significantly as they grow. If you need a BMI assessment for a child, consult your pediatrician.
How can I improve my BMI?
A balanced diet and regular physical activity are the most effective and sustainable ways to achieve and maintain a healthy BMI. Focus on whole foods, adequate protein, and consistent movement rather than extreme diets. Small, gradual changes tend to produce lasting results. The Kalori app can help you track your food intake and monitor progress over time, making it easier to stay on course toward your goals.
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