Body mass index (BMI) is a calculation used to determine an adult's overall fatness or thinness. The World Health Organization defines a healthy BMI as falling between 18.5 and 24.9.
Underweight Parameters
Some practitioners classify a BMI below 20 (rather than 18.5) as underweight; others set a threshold of 19. The parameters that define low weight may vary among nations.
Overweight Parameters
The World Health Organization considers a body mass index exceeding 25 to be overweight; WHO also designates four categories of obesity, including pre-obese, obese class I, obese class II and obese class III.
International Variations
People of Asian or Pacific ethnicity may be overweight by practical standards, even if their BMI calculations fall within WHO's "normal" range. In Singapore, a BMI above 23 is considered overweight.
Considerations
While there are some unofficial BMI formulas designed to accommodate age, gender, lifestyle and other variables, there are no widely accepted variations of the BMI formula.
Limitations
The body mass index formula may not accurately estimate percentage body fat. For example, an athlete may have an "overweight" BMI even if she has a body fat percentage.
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