BMI Calculator

Body Mass Index (BMI)

Body Mass Index (BMI) is a globally recognized screening tool used to estimate whether your weight is healthy for your height. According to the World Health Organization, over 2.5 billion adults were overweight in 2022, including 890 million living with obesity. While BMI does not directly measure body fat, it helps identify potential health risks related to underweight, overweight, or obesity.

According to WHO, over 2.5 billion adults were overweight in 2022, including 890 million living with obesity.

BMI Classification

Use the chart below to interpret your BMI result.

Note: WHO defines overweight as a BMI ≥ 25 and obesity as a BMI ≥ 30 for adults.

BMI classification chart for adults
BMI Classification
< 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30.0 – 34.9 Obesity Class I
35.0 – 39.9 Obesity Class II
≥ 40.0 Obesity Class III

Limitations of BMI

  • BMI does not distinguish between muscle and fat mass, so athletes or muscular individuals may be classified as overweight or obese.
  • It may underestimate body fat in older adults or those with low muscle mass.
  • BMI does not account for age, sex, ethnicity, or body composition differences.
  • It is a screening tool, not a diagnostic measure of health or body fatness.

Health Risks of High BMI

Higher-than-optimal BMI is associated with increased risk of noncommunicable diseases such as type 2 diabetes, cardiovascular disease, certain cancers, and respiratory disorders. In 2021, elevated BMI contributed to an estimated 3.7 million deaths globally.

Causes of Overweight and Obesity

  • Energy imbalance: Consuming more calories than are expended through activity.
  • Environmental and societal factors: Limited access to healthy food, urban design, and sedentary lifestyles.
  • Genetic and medical contributors: Family history, certain medical conditions, and medications.

Obesity is often driven by a combination of factors including poor diet, physical inactivity, genetic predisposition, and environmental influences that limit access to healthy food and safe spaces for movement.

  • Obesity has more than doubled worldwide since 1990.
  • In 2022, 43% of adults were overweight and 16% were obese.
  • Childhood obesity is rising rapidly, especially in low- and middle-income countries.

Frequently Asked Questions (FAQ)

BMI is a useful screening tool but not a diagnostic measure. It does not distinguish between muscle and fat mass, so results may not be accurate for athletes, older adults, or those with atypical body compositions.

BMI calculators are intended for adults. They may not be suitable for children, pregnant women, athletes, or people with high muscle mass or certain medical conditions.

You should check your BMI when your weight or height changes significantly, or as part of regular health assessments.

Alternatives include waist-to-height ratio, body fat percentage, waist circumference, and other clinical assessments that provide more detail about body composition.

BMI for children and teens is interpreted differently and uses age- and sex-specific percentiles. Consult a pediatrician for accurate assessment.

References

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