Reading a BMI percentile
For children, BMI is turned into a percentile for their age and sex. Below the 5th percentile is underweight, the 5th to under the 85th is a healthy weight, the 85th to under the 95th is overweight and the 95th or above is obesity. A child at the 60th percentile has a higher BMI than 60 out of 100 children of the same age and sex in the reference data.
Measuring children at home
- Shoes off, heels together and back against a wall; place a book flat on the head and mark the wall.
- Weigh in light clothes on a hard floor; for toddlers, weigh an adult holding the child and subtract the adult’s weight.
- Note the exact age in years and months — the calculator uses both.
Talking with children about weight
Keep BMI results between adults. Children respond better to talk about energy, strength and enjoying food than to numbers or labels. Focus on family habits — regular meals, water instead of sugary drinks, active play and enough sleep — rather than dieting. If a result worries you, a doctor or school nurse can review growth over several measurements.
What “severe obesity” means for children
For children, severe obesity is defined as a BMI at or above 120% of the 95th percentile for their age and sex. Because the standard growth charts stop at the 97th percentile, this extra definition helps doctors follow children with the highest BMI over time. The calculator flags it automatically when it applies.