Child & Teen BMI Percentile Calculator
BMI read against CDC growth reference percentiles for children and teenagers aged 2 to 20.
A child's BMI cannot be read against adult bands. Children change shape as they grow, and boys and girls do it differently, so the same BMI means different things at different ages. This calculator compares the BMI with the CDC growth reference for children of the same age and sex and reports a percentile.
How this is worked out
The CDC weight-status categories for ages 2 to 19 are: below the 5th percentile underweight, 5th to below 85th healthy weight, 85th to below 95th overweight, and 95th and above obesity. The percentile is calculated with the CDC's published LMS parameters — a power transformation (L), a median (M) and a coefficient of variation (S) for each age in months — which convert a BMI into a z-score and then into a percentile.
The reference data shipped with this calculator is the CDC 2000 BMI-for-age table, thinned to roughly two-month steps and interpolated in between. That introduces a difference of well under one percentile point against the full table.
A single percentile is far less useful than a series of them. Growth is a trajectory, and a child tracking steadily along the 70th percentile is in a very different situation from one who has climbed from the 40th to the 90th in a year. Take any result that concerns you to a paediatrician with the child's growth chart, rather than acting on it alone.
This calculator runs entirely in your browser. Nothing you enter is transmitted to us, saved on our servers, or shared with anyone.
Common questions
Why use percentiles instead of the adult BMI bands?
Because a healthy BMI for a six-year-old is around 15 and for a seventeen-year-old around 21. Percentiles compare a child only with children of the same age and sex.
My child is in the 90th percentile. Is that a problem?
It falls in the CDC "overweight" band, but it is a screening signal, not a diagnosis. Children who are tall for their age, very muscular, or in the middle of a growth spurt can read high. A paediatrician looking at the whole growth chart is the right next step.
Does this work for babies?
No. BMI-for-age reference data starts at 24 months. Below that, weight-for-length charts are used instead, and those are best read by a health visitor or paediatrician.