BMI Calculator by Age
The healthy BMI range varies by life stage. Find out what applies to your age group.
Children and Teens: Percentiles Instead of Fixed Numbers
For children and teenagers under 18, there are no fixed BMI cutoff values as with adults. Instead, the BMI value is classified into age- and sex-specific percentiles. A child is considered overweight if their BMI is above the 90th percentile, and underweight if below the 10th percentile. Growth phases and hormonal changes during puberty make fixed thresholds unreliable.
Adults 18–65: Standard Values 18.5–24.9
For adults between 18 and 65, WHO standard values apply: underweight below 18.5, normal weight 18.5–24.9, overweight 25–29.9, obesity from 30. These values were validated on large adult populations and are considered a reliable first reference point – although they do not account for muscle mass, body fat distribution or ethnic differences.
Seniors 65+: A Slightly Higher BMI May Be Protective
For people aged 65 and over, many studies recommend a slightly higher BMI of 23–27 as optimal. The reason: muscle mass decreases with age (sarcopenia), and a too-low BMI can indicate muscle loss and malnutrition. Unintentional weight loss in old age is a warning sign. At the same time, muscle loss makes the standard BMI less meaningful – a 70-year-old with BMI 24 can still have sarcopenia.
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