Child and Teen BMI Percentile Calculator
By Rick Campbell · Updated · Sourced to primary literature · Not medical advice
A child's body mass index means nothing on its own. A BMI of 17 is high for a four-year-old, squarely normal for a twelve-year-old and low for a nineteen-year-old, because the amount of body fat that is healthy changes continuously through childhood and puberty. The adult cut-offs of 18.5, 25 and 30 simply do not apply before growth finishes.
So children are assessed against a reference population of the same age and sex. This calculator places a child's BMI on the US Centers for Disease Control growth reference and reports the percentile: the proportion of children of that exact age and sex whose BMI falls below this one. It covers ages 2 to 20.
It also shows the numbers behind the percentile: the z-score, the BMI at each threshold for that age, and the percentage of the 95th percentile that the CDC now recommends for values far above the reference range. What it will not do is label your child.
In brief
- Children's BMI is read as a percentile against others of the same age and sex, never against the adult 18.5/25/30 cut-offs.
- The CDC bands are: below the 5th percentile underweight, 5th to below 85th healthy weight, 85th to below 95th overweight, 95th and above obesity.
- Above the 97th percentile the percentile scale compresses, so the CDC uses percent-of-the-95th-percentile instead: 120% marks class 2 and 140% class 3 obesity.
- A single reading is a snapshot; children grow in bursts, and the trajectory across a growth chart matters far more than one measurement.
- The right next step for any result outside the healthy band is a GP, paediatrician or child health nurse, not a diet.
Calculator
What you'll see here
The child's BMI, the percentile it sits at on the CDC growth reference for their exact age in months and sex, the weight-status band that percentile falls in, the BMI values that mark every CDC threshold at that age with the child's own value placed among them, how far an ordinary measuring error would move the answer, and the BMI that would keep them on this same centile a year from now.
| Category | Range | Absolute alternative |
|---|---|---|
| Underweight | Below the 5th percentile | |
| Healthy weight | 5th to below the 85th percentile | |
| Overweight | 85th to below the 95th percentile | |
| Obesity | At or above the 95th percentile | |
| Severe obesity, class 2 | At or above 120% of the 95th percentile | …or a BMI of 35 |
| Severe obesity, class 3 | At or above 140% of the 95th percentile | …or a BMI of 40 |
These are screening categories drawn on a reference distribution, not diagnoses. The two severe-obesity classes are expressed as a percentage of the 95th percentile because ordinary percentiles stop distinguishing between children once they pass about the 97th; the CDC lists an absolute BMI alternative for each.
CDC BMI thresholds by age: boys
The BMI value at each CDC percentile line. A child's BMI is read against the row for their age, not against the adult cut-offs of 18.5, 25 and 30.
| Age | 5th (underweight below) | 50th (median) | 85th (overweight from) | 95th (obesity from) |
|---|---|---|---|---|
| 2 years | 14.7 | 16.6 | 18.2 | 19.3 |
| 4 years | 14 | 15.6 | 16.9 | 17.8 |
| 6 years | 13.7 | 15.4 | 17 | 18.4 |
| 8 years | 13.8 | 15.8 | 17.9 | 20 |
| 10 years | 14.2 | 16.6 | 19.4 | 22.1 |
| 12 years | 15 | 17.8 | 21 | 24.2 |
| 14 years | 16 | 19.1 | 22.6 | 26 |
| 16 years | 17.1 | 20.5 | 24.2 | 27.5 |
| 18 years | 18.2 | 21.9 | 25.6 | 28.9 |
| 19 years | 18.7 | 22.5 | 26.3 | 29.7 |
Notice how the median BMI falls from age 2 to about age 6 and then climbs again, the "adiposity rebound". It is why a fixed number could never work for children.
Why children get percentiles instead of categories
Body fatness follows a predictable arc through childhood. It falls from toddlerhood to around age five or six (the point clinicians call the adiposity rebound), then climbs steadily through the school years and into adolescence, with the timing differing between boys and girls by a year or more. A fixed threshold applied across that arc would call most six-year-olds underweight and most seventeen-year-olds overweight.
The reference charts solve this by asking a different question: not 'is this number high' but 'how does this measurement compare with other children of the same age and sex'. The answer comes back as a percentile. A child at the 60th percentile has a BMI higher than about 60 in every 100 children in the reference population, and lower than the other 40.
How the percentile is worked out
The CDC publishes three parameters for every age in months and each sex, known as L, M and S. M is the median BMI at that age, S describes the spread, and L is a skew term that corrects for the fact that BMI distributions are not symmetrical: there is far more room above the median than below it. Together they convert a BMI into a z-score, which is then read off the normal distribution as a percentile.
This calculator interpolates the published parameters between the CDC's half-month points, so a child of ten years and seven months is measured against ten years and seven months, not rounded to the nearest year. That matters more than it sounds: between ages 10 and 11 the 95th percentile BMI moves by roughly half a point.
What the bands mean
The CDC's weight-status categories for ages 2 to 19 are: below the 5th percentile is underweight, the 5th up to the 85th is healthy weight, the 85th up to the 95th is overweight, and the 95th percentile or above is obesity. These are screening categories drawn on a reference distribution, not diagnoses; a fit, muscular teenager and a sedentary one can land in the same band for very different reasons.
Above the 95th percentile, ordinary percentiles stop being informative because they crowd towards 99: a child well above the reference range and one far above it both read '99th'. The CDC therefore recommends expressing severe obesity as a percentage of the 95th percentile. At or above 120% of that line is class 2 obesity, and at or above 140% is class 3. This page shows that figure alongside the percentile whenever the value sits high.
How to measure a child accurately
Measure height without shoes, heels together, back against a wall, looking straight ahead with the head level. Read to the nearest half centimetre. Weigh in light clothing, without shoes, on a firm floor rather than carpet, ideally at the same time of day each time. For younger children who will not stand still, two people and a second attempt is normal.
At these ages small measurement errors matter more than they do in adults, because the reference curves are steep. A two-centimetre height error moves a ten-year-old's BMI by roughly half a point, which can shift the percentile by several points near the middle of the distribution.
What a result outside the healthy band actually means
It means the measurement sits outside the middle of the reference distribution, and that is worth a conversation with someone who can examine your child and look at their growth history. It does not mean a diet. For children who are still growing, clinicians usually aim to hold weight roughly steady and let height catch up, which changes the ratio without any of the risks that restriction carries at this age.
The evidence on what works is consistent and unglamorous: family-wide changes rather than a plan aimed at one child, regular meals rather than restriction, sleep, and activity that the child actually enjoys. Singling one child out at the dinner table is associated with worse outcomes, including disordered eating later.
- Growth charts are for tracking trajectory over time; one point on a chart is a dot, not a line.
- Puberty shifts body composition rapidly, and BMI-for-age cannot see whether a change is muscle or fat.
- Children with a high BMI who are also very tall for their age often have a different explanation than those who are not.
Where the CDC charts come from, and their limits
The CDC growth reference was built from US national survey data collected between 1963 and 1994, deliberately excluding the more recent surveys in which obesity prevalence rose sharply; the intention was a stable reference, not a description of today's children. The World Health Organization publishes its own growth standards for ages 5 to 19, based on a multi-country sample, and many countries outside the US use those instead. The two disagree by a few percentile points, particularly in adolescence.
Neither reference measures body fat. BMI-for-age is a screen that flags children worth a closer look, and it misclassifies in both directions: a muscular young athlete can read high while carrying little fat, and a child with low muscle mass can read normal while carrying a lot. If the number and the child in front of you disagree, trust the examination.
How it's calculated
Body mass index
BMI = weight (kg) ÷ height (m)²
Identical arithmetic to the adult calculation; it is the interpretation that differs.
CDC LMS z-score
z = ((BMI ÷ M)^L − 1) ÷ (L × S) · when L = 0: z = ln(BMI ÷ M) ÷ S
L, M and S are the CDC's published skew, median and coefficient-of-variation parameters for that exact age in months and sex.
Percentile
percentile = Φ(z) × 100, where Φ is the standard normal cumulative distribution
A z-score of 0 is the 50th percentile; 1.645 is the 95th.
Percent of the 95th percentile (severe obesity metric)
%P95 = BMI ÷ (BMI at the 95th percentile for that age and sex) × 100
Class 2 obesity from 120%, class 3 from 140%, used because percentiles compress at the top of the distribution.
Worked example: a boy of 10 years and 6 months, 142 cm and 38 kg
- Convert height to metres: 142 cm = 1.42 m.
- Compute BMI: 38 ÷ (1.42 × 1.42) = 38 ÷ 2.0164 = 18.8.
- Look up the CDC parameters for boys at 126 months and interpolate between the published points.
- Apply the LMS transform to turn 18.8 into a z-score of roughly 0.9.
- Read the normal distribution: a z of 0.9 is about the 82nd percentile.
- Interpret: the 82nd percentile sits inside the healthy-weight band, which runs from the 5th up to the 85th. That is close to the upper boundary, which is worth watching over the next year rather than acting on today.
Where this number is used in the real world
- Routine child health checks, where BMI-for-age is plotted on a growth chart alongside height and weight curves.
- School health screening programmes in several countries, which report percentile bands rather than raw BMI.
- Paediatric clinics assessing whether growth is tracking along a consistent centile or crossing lines.
- Referral thresholds for weight-management and endocrine services, which are usually written in percentile terms.
- Research and public-health surveillance, where population prevalence of overweight and obesity in children is defined by these exact cut-offs.
- Parents checking whether a GP's comment about their child's growth chart matches the numbers they have at home.
Frequently asked questions
What is a healthy BMI percentile for a child?
The CDC's healthy-weight band runs from the 5th percentile up to but not including the 85th, for every age from 2 to 19 and for both sexes. Below the 5th is classed as underweight and warrants a growth assessment; the 85th to the 95th is overweight; the 95th and above is obesity. These are screening bands drawn on a reference population, not a diagnosis, and a child sitting near either boundary is usually best watched over time rather than acted on from one reading.
Why can't I use the adult BMI categories for my child?
Because the amount of body fat that is normal changes continuously as children grow. Body fatness falls from toddlerhood to about age six, then rises through the school years and adolescence, and the timing differs between boys and girls. A fixed threshold of 25 would classify almost no children as overweight at age six and a great many at eighteen, for reasons that have nothing to do with health. Age- and sex-specific percentiles are the only defensible reading before growth finishes.
My child is at the 95th percentile. What should I do?
Make an appointment with your GP, paediatrician or child health nurse, and take any previous heights and weights you have. They can plot the trajectory, examine your child, check whether growth is otherwise normal, and rule out the handful of medical causes worth excluding. What the evidence does not support is putting a growing child on a restrictive diet: clinicians usually aim to hold weight steady while height increases, alongside family-wide changes to meals, sleep and activity.
What does percent of the 95th percentile mean?
It is the child's BMI expressed as a percentage of the BMI that marks the 95th percentile at their age and sex. It exists because ordinary percentiles stop distinguishing between children once they pass about the 97th: everything reads as 99th. At or above 120% of the 95th percentile is classed as class 2 obesity and at or above 140% as class 3, which is how paediatric services describe severe obesity and decide on referral.
Does this calculator use the CDC or WHO growth charts?
The CDC growth reference, which covers ages 2 to 20 and is the standard in the United States. The World Health Organization publishes separate growth standards, used as the default in many other countries, which are based on a multi-country sample and read a little differently in adolescence. If your health service plots on WHO charts, expect percentiles from this page to differ by a few points; ask which reference your clinician is using.
Is BMI-for-age accurate for muscular or athletic children?
It has the same blind spot as adult BMI, and the same magnitude of error. BMI-for-age counts total mass against height and cannot distinguish muscle from fat, so a young athlete in a strength or contact sport can sit above the 85th percentile while carrying very little body fat. The pattern is usually obvious on examination, which is another reason the percentile is a prompt for a professional look rather than a conclusion in itself.
How often should a child's BMI be checked?
Once or twice a year is plenty for most children, usually as part of a routine health check, and the value is in the trend rather than the individual reading. Children grow in bursts: a child can gain weight ahead of a height spurt and cross a percentile line for a few months before returning to their usual track. Frequent weighing at home is rarely useful and, for older children especially, can make weight more salient than it needs to be.
Keep going
A single number rarely tells the whole story. Alongside the child BMI result, the BMI calculator, the healthy weight range calculator, the waist-to-height calculator and the BSA calculator each add a different angle on the same measurements. For the reasoning behind the numbers, read BMI explained and 2025 obesity definition.
Sources
- CDC. BMI-for-age growth chart parameters (extended, 2022 release of the 2000 reference). www.cdc.gov/growthcharts/percentile_data_files.htm
- CDC. About Child & Teen BMI: weight status categories for ages 2 to 19. www.cdc.gov/bmi/child-teen-calculator/
- Kuczmarski RJ, et al. 2000 CDC growth charts for the United States: methods and development. Vital Health Stat 11, 2002;246:1–190. www.cdc.gov/nchs/data/series/sr_11/sr11_246.pdf
- Kelly AS, Barlow SE, Rao G, et al. Severe obesity in children and adolescents: identification, associated health risks, and treatment approaches: a scientific statement from the American Heart Association. Circulation 2013;128:1689–1712. doi.org/10.1161/CIR.0b013e3182a5cfb3
- WHO. Growth reference data for 5–19 years: BMI-for-age. www.who.int/tools/growth-reference-data-for-5to19-years/indicators/bmi-for-age
Cite this page
Quoting a figure from here in an article, a report or a piece of coursework? Use whichever of these your style guide asks for.
- APA
- Campbell, R. (2026). Child and Teen BMI Percentile Calculator. Body Stats. https://bodystats.co/app/child-bmi-calculator
- Plain text
- “Child and Teen BMI Percentile Calculator”, Body Stats, last updated 12 September 2026, https://bodystats.co/app/child-bmi-calculator
Every formula and threshold on this page is written out with its primary source on our methodology page. These results are informational and educational, not a diagnosis or a substitute for professional advice. See the medical disclaimer.
Last updated . Written by Rick Campbell; not medically reviewed. See review status.