BMI Percentile Calculator
Child and teen BMI percentile for ages 2 to 19 from the official CDC LMS growth-chart parameters, with the CDC weight-status category and the curves for that age.
BMI Percentile Calculator: with the default inputs, bmi is 18.6.
BMI-for-age curves differ substantially between boys and girls.
Percentiles move quickly in childhood, so the extra months matter.
Weight in kilograms divided by height in metres squared.
- CDC weight status
- Healthy weight (5th to 84th percentile)
- BMI-for-age percentile
- 78.9The share of US children of the same age and sex with a lower BMI, on the CDC 2000 reference.
- BMI z-score
- 0.8
- Median BMI for this age and sex
- 16.6
- 85th percentile BMI
- 19.4
- 95th percentile BMI
- 22.1
- Share of the 95th percentile
- 84%CDC uses 120% of the 95th percentile as the threshold for severe obesity.
- Age in months
- 120
Assumptions
- CDC 2000 BMI-for-age reference, using the published L, M and S parameters linearly interpolated between half-month reference ages.
- Percentiles come from the standard normal CDF of the LMS z-score and are clamped for display to the 0.1st–99.9th range, where the method stops discriminating.
- Covers ages 24 to 240 months only; WHO weight-for-length charts apply below 2, adult BMI categories from 20.
- BMI is a screen for body fatness, not a measurement of it.
| Age (years) | 5th (underweight below) | 50th (median) | 85th (overweight from) | 95th (obesity from) |
|---|---|---|---|---|
| 2 | 14.7 | 16.6 | 18.2 | 19.3 |
| 3 | 14.3 | 16 | 17.4 | 18.3 |
| 4 | 14 | 15.6 | 16.9 | 17.8 |
| 5 | 13.8 | 15.4 | 16.8 | 17.9 |
| 6 | 13.7 | 15.4 | 17 | 18.4 |
| 7 | 13.7 | 15.5 | 17.4 | 19.1 |
| 8 | 13.8 | 15.8 | 17.9 | 20 |
| 9 | 14 | 16.1 | 18.6 | 21 |
| 10 | 14.2 | 16.6 | 19.4 | 22.1 |
Computed from the CDC LMS parameters at each exact birthday.
How this is worked out
The formula
BMI = weight (kg) ÷ height (m)² CDC BMI-for-age, using the LMS parameters for the child's exact age and sex: z = ((BMI ÷ M)^L − 1) ÷ (L × S) (or ln(BMI ÷ M) ÷ S when L = 0) percentile = Φ(z) × 100 (Φ = standard normal CDF) BMI at percentile p = M × (1 + L × S × z_p)^(1/L) L = Box-Cox power, M = median BMI, S = coefficient of variation — all read from the CDC growth-chart file and interpolated between its half-month reference ages.
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Sex
- BMI-for-age curves differ substantially between boys and girls.Boy · Girl
- Age
- A number.from 2 to 19 · whole numbers only · defaults to 10
- …and months
- Percentiles move quickly in childhood, so the extra months matter.from 0 to 11 · whole numbers only · defaults to 0
- Height
- A number.in in, cm, m · from 20 to 90 · defaults to 55
- Weight
- A number.in lb, kg, st · from 10 to 500 · defaults to 80
What you get back
- BMImain answer
- Weight in kilograms divided by height in metres squared.
- CDC weight status
- BMI-for-age percentile
- The share of US children of the same age and sex with a lower BMI, on the CDC 2000 reference.
- BMI z-score
- Median BMI for this age and sex
- 85th percentile BMI
- 95th percentile BMI
- Share of the 95th percentile
- CDC uses 120% of the 95th percentile as the threshold for severe obesity.
- Age in months
What this assumes
- CDC 2000 BMI-for-age reference, using the published L, M and S parameters linearly interpolated between half-month reference ages.
- Percentiles come from the standard normal CDF of the LMS z-score and are clamped for display to the 0.1st–99.9th range, where the method stops discriminating.
- Covers ages 24 to 240 months only; WHO weight-for-length charts apply below 2, adult BMI categories from 20.
- BMI is a screen for body fatness, not a measurement of it.
About this calculator
A child's BMI cannot be read against the adult 18.5 / 25 / 30 thresholds. Body composition changes enormously between the ages of two and twenty, and it changes differently for boys and girls: median BMI actually falls through early childhood, bottoms out around age five or six, and then climbs steadily through adolescence. A BMI of 19 is high for a six-year-old and unremarkable for a sixteen-year-old.
So paediatric BMI is expressed as a percentile against a reference population of the same age and sex. This calculator computes it from the official CDC 2000 growth-chart parameters — the same L, M and S values the CDC publishes for clinical software — rather than approximating from a printed chart.
How to use it
Enter the child's sex, exact age in years and months, height and weight. Age precision matters: the curves move fast enough in childhood that six months can shift a percentile by several points. Measure height without shoes and weight in light clothing, and use the same scale each time — the trend across visits carries far more information than any single reading.
The CDC categories
- Underweight — below the 5th percentile
- Healthy weight — 5th to below the 85th
- Overweight — 85th to below the 95th
- Obesity — at or above the 95th
- Severe obesity — at or above 120% of the 95th percentile, or a BMI of 35, whichever is lower
That last category exists because the percentile scale stops being useful at the top. Once a child is above about the 99th percentile, the z-score method compresses enormous differences in BMI into a sliver of percentile, so CDC recommends expressing very high values as a share of the 95th percentile instead. That figure is shown above and is the one clinicians now track for children with obesity.
What the reference actually is
The CDC 2000 charts were built from US national survey data gathered between 1963 and 1994, with the heaviest recent data deliberately excluded from the BMI charts so the upper curves would not drift with the obesity epidemic. They are a description of a historical US population, not a statement about health. A child on the 90th percentile is heavier than 90% of American children measured decades ago — that is all the number says.
Limits worth knowing
BMI does not measure body fat. It cannot tell muscle from fat, it reads high for stocky and athletic builds, and it varies systematically with limb-to-trunk proportions across ancestries. Below age two, clinicians use WHO weight-for-length charts instead; the WHO growth standards are also preferred internationally for ages 0–5 because they describe optimal growth rather than an observed population. From age 20, adult BMI categories take over.
This tool is a screen. A percentile above the 95th or below the 5th is a reason to talk to a paediatrician, who will look at growth velocity, blood pressure, family history and pubertal stage — none of which a single number can carry.
Frequently asked questions
▸What is a healthy BMI percentile for a child?
The CDC classes the 5th to 84th percentile as healthy weight, 85th to 94th as overweight, and 95th or above as obesity. Below the 5th percentile is underweight.
▸Why can't I use adult BMI categories for my child?
Because body composition changes with age and differs by sex. Median BMI falls until about age six and then rises through the teens, so a fixed cut-off would misclassify children at both ends of the range.
▸What does the 95th percentile mean?
The child's BMI is higher than 95% of US children of the same age and sex in the CDC reference population. It is the CDC threshold for obesity in children and teens.
▸What is 120% of the 95th percentile?
The CDC threshold for severe obesity. Above roughly the 99th percentile the percentile scale compresses, so expressing BMI as a share of the 95th-percentile value keeps distinguishing between children whose percentiles all round to 99.
▸Does a high BMI percentile mean my child is unhealthy?
Not on its own. BMI does not measure body fat and reads high for muscular and stocky builds. It is a screening flag: a result above the 95th or below the 5th percentile is a reason for a paediatric review, not a diagnosis.
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