BMI Chart for Children — Percentiles by Age

A child’s BMI is never read against the adult ranges. It is converted into a percentile — a comparison with thousands of other children of the same age and the same sex — and the percentile, not the raw number, carries the category. This is why a chart of fixed BMI bands for children does not exist, and why the one you may have seen is not from a health authority.

Percentile of BMI-for-age	Category
Below the 5th	Underweight
5th to 84th	Healthy weight
85th to 94th	Overweight
95th and above	Obesity

These are the categories the American Academy of Pediatrics publishes for children and teens. The 95th percentile means the child’s BMI is higher than that of 95 out of 100 children of the same age and sex in the reference population — a statement about position in a distribution, not about a number of kilograms per square meter.

Why a moving target instead of a fixed range

Expected BMI is not flat through childhood. It falls through the preschool years, reaches a low point somewhere around age five or six, and then climbs steadily through adolescence — a normal pattern of growth, not a warning sign. A BMI of 17 sits well above the median for a six-year-old and below it for a sixteen-year-old.

Any fixed table would therefore have to be wrong for most ages to be right for one. Percentiles solve that by re-anchoring the comparison at every age, which is also why the child’s exact age in months, and not just in years, is part of the reading.

Two references, and where they switch

US practice uses two different references, and the switch happens at two years old. CDC’s published recommendation is to use the 2006 WHO international growth charts for children under 24 months and the CDC growth charts for ages 2 through 19. The reason given for the first is that the WHO reference population was predominantly breastfed, which matches current infant feeding guidance.

Two consequences follow. BMI-for-age percentiles start at age 2, since infants under two are tracked by weight-for-length rather than by BMI at all. And the screening cutoffs on the WHO charts are not the same lines: the recommendation there is the 2.3rd and 97.7th percentiles, equivalent to two standard deviations either side of the median, rather than the 5th and 95th.

WHO, for its part, defines overweight in ages 5 to 19 as BMI-for-age more than one standard deviation above its reference median and obesity as more than two — the same idea expressed in standard deviations instead of percentiles.

A note on sourcing: CDC’s own web pages block automated access, so nothing here is quoted from them. The growth-chart recommendation above is taken from the CDC recommendation as published in MMWR and indexed in PubMed, and the percentile categories from the American Academy of Pediatrics.

What a parent can actually do with the number

Calculating the raw BMI at home is the easy half and the half that decides nothing. Height in particular is the weak link: a toddler measured on a bathroom scale platform, or a nine-year-old measured in shoes, produces an error that shifts the percentile far more than it shifts an adult’s BMI, because children are shorter and the height is squared.

So the sequence that works is: let the measurement happen at the checkup, ask for the percentile rather than the number, and ask what the last two or three points did. A stable percentile is reassuring even when it is not the 50th. Movement across lines is the finding.

And one thing not to do at home: put a child on a restrictive diet on the strength of a percentile. Growth needs energy, and changes to a child’s eating are made with a pediatrician or a pediatric dietitian, not from a chart.

Where the adult table starts to apply

Somewhere in the late teens the two systems meet. Growth charts run through 19, and the adult classification is written for ages 20 and up, so the changeover is a matter of a year or two rather than a birthday. For those adult ranges, see the BMI chart; for how the index is read at the other end of life, see the BMI chart for seniors.

This content is informational and does not replace evaluation by a pediatrician.