Child & Teen BMI Percentile Calculator
BMI-for-age percentile and weight status for ages 2–19, plotted on a CDC growth chart.
Enter the child’s age, height and weight.
BMI-for-age growth chart
CDC 2000 percentile curves; above the 95th, the dashed lines mark 120% and 140% of the 95th percentile (AAP class 2 and 3 obesity).
Cut-offs at this age, and the weight they mean at this height
| Cut-off | BMI | Weight |
|---|
Children are still growing, so these weights change as they get taller. They show what the cut-offs mean today — not a weight target.
How it was calculated
For general information only, not medical advice. Consult a qualified health professional for advice about your situation.
About the Child & Teen BMI Percentile Calculator
Children’s BMI changes as they grow, so a child’s BMI is compared with other children of the same age and sex and given as a percentile. A BMI at the 70th percentile is equal to or higher than 70% of children of that age and sex in the reference population.
This calculator uses the CDC 2000 growth charts (ages 2 to 19) and, above the 95th percentile, CDC’s 2022 extended BMI-for-age method, which describes very high BMIs far better than the original charts. You get the percentile, the BMI z-score, the BMI as a % of the 95th percentile, the weight status used by CDC and the American Academy of Pediatrics (including class 2 and class 3 obesity), the cut-off BMIs for your child’s age — and a growth chart with your child’s point on it.
How to use it
- Choose girl or boy and enter the age — completed years and months, or the date of birth and the date the child was measured (most precise).
- Enter the height and weight in kg and cm or lb and ft/in. Measure standing height without shoes and weight in light clothing.
- Read the BMI-for-age percentile, weight status, z-score and % of the 95th percentile. The growth chart shows where the BMI sits among children of the same age and sex.
- Use Copy result or Download CSV to keep the numbers or share them with your child’s doctor.
Examples
z-score 1.42 · 92.2nd percentile · Overweight (85th to below the 95th)
95th percentile at this age is 17.8 · extended percentile 99.77, z-score 2.83 · 126.8% of the 95th — class 2 obesity
BMI 26.6 · about the 96th percentile · Obesity (class 1), as in CDC’s own example
BMI 16.5 · 47.9th percentile · z-score −0.05 · Healthy weight
How the percentile is worked out
CDC publishes three numbers for every month of age from 2 to 20, separately for boys and girls: L (a Box-Cox power that corrects for skew), M (the median BMI) and S (a coefficient of variation). The calculator interpolates them to the child’s exact age, as CDC’s own programs do, then:
- z-score = ((BMI ÷ M)^L − 1) ÷ (L × S)
- percentile = Φ(z) × 100, where Φ is the standard normal distribution
Age is counted the CDC way: days since birth ÷ 30.4375 when you give dates, or completed months + 0.5 when you give years and months (a child who is 9 years 6 months is treated as 114.5 months, the middle of that month). If you leave the months empty, CDC’s rule for an age in completed years applies: years × 12 + 6, the middle of that year.
Above the 95th percentile: CDC’s extended method (2022)
The 2000 charts were built from children measured mostly between 1963 and 1980, and their LMS z-scores flatten out at very high BMIs — for boys aged 7 to 15, the original z-score cannot exceed about 3.3 however high the BMI. In 2022 CDC therefore switched to extended percentiles for BMIs above the 95th percentile, based on a half-normal distribution fitted to children with obesity:
- percentile = 90 + 10 × Φ((BMI − P95) ÷ σ)
- z-score = Φ⁻¹(percentile ÷ 100)
where P95 is the 95th-percentile BMI for the age and σ comes from CDC’s regressions on age in years: girls σ = 0.8334 + 0.3712 × age − 0.0011 × age², boys σ = 0.3728 + 0.5196 × age − 0.0091 × age². Up to the 95th percentile nothing changes. Above it, results differ from calculators built before 2022: the extended z-score is lower just above the 95th percentile — up to roughly 125–150% of it, depending on age and sex — and higher beyond that, where the original z-scores level off.
Weight status categories
CDC categories for ages 2 through 19, based on the BMI-for-age percentile:
- Underweight: below the 5th percentile
- Healthy weight: 5th to below the 85th percentile
- Overweight: 85th to below the 95th percentile
- Obesity: 95th percentile or above
- Severe obesity: 120% of the 95th percentile or more, or a BMI of 35 or more
The American Academy of Pediatrics (2023 guideline) splits obesity further: class 2 is 120% to below 140% of the 95th percentile, or BMI 35 to below 40; class 3 is 140% of the 95th percentile or more, or BMI 40 or more — whichever is lower. Below 120% it is class 1.
What “% of the 95th percentile” means
It is the child’s BMI divided by the 95th-percentile BMI for their age and sex, × 100. CDC gives this example: the 95th percentile for a 60-month-old boy is 17.9, so a BMI of 21.3 is 119% of it (100 × 21.3 ÷ 17.9). Because it keeps rising in step with BMI, it still separates children whose percentiles are all crowded close to 100 — CDC uses it to define severe obesity and the AAP to grade obesity classes.
CDC, WHO or IAP charts?
- Under 2 years: CDC recommends the WHO growth charts, so this calculator does not accept ages under 2.
- 2 to 19 years: the CDC charts used here are a US reference.
- India: the Indian Academy of Pediatrics recommends its revised 2015 IAP charts for Indian children aged 5 to 18, where overweight and obesity are defined by the adult-equivalent BMI 23 and 27 lines, and the WHO standards below 5. A child can fall in a different category on IAP and CDC charts, so ask your paediatrician which chart they use.
- 20 and over: use the adult BMI calculator.
Sources
- CDC, BMI-for-age LMS data file and Extended BMI-for-age growth charts data file — L, M, S and σ values and worked examples
- CDC, SAS program for the CDC growth charts — age conventions, extended BMI, severe obesity, implausible-value flags
- CDC, Child and Teen BMI Categories
- Kuczmarski RJ et al. 2000 CDC growth charts for the United States: methods and development. Vital Health Stat 11(246), 2002
- Flegal KM, Cole TJ. Construction of LMS parameters for the CDC 2000 growth charts. NHSR No. 63, 2013
- Wei R, Ogden CL, Parsons VL, Freedman DS, Hales CM. A method for calculating BMI z-scores and percentiles above the 95th percentile of the CDC growth charts. Ann Hum Biol 2020;47:514-21
- Hampl SE et al. Clinical practice guideline for the evaluation and treatment of children and adolescents with obesity. Pediatrics 2023;151:e2022060640
- IAP Growth Charts Committee. Revised IAP growth charts for height, weight and BMI for 5- to 18-year-old Indian children. Indian Pediatr 2015;52:47-55
Limitations
- BMI-for-age is a screening measure, not a diagnosis: it does not measure body fat and cannot tell muscle from fat.
- The CDC reference comes from US children measured mostly between 1963 and 1980; other national charts (WHO, IAP) can place the same child differently.
- One measurement is a snapshot. Doctors look at how a child’s percentile changes over time, together with family history and other health measures.
- Ages 2 years to 19 years 11 months, heights 50–250 cm and weights 2–300 kg are accepted. BMIs CDC would flag as biologically implausible are shown with a warning to check the measurements.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
What is a BMI-for-age percentile?
It ranks a child’s BMI against children of the same age and sex in the CDC reference population. The 85th percentile means the BMI is equal to or higher than 85% of them. Percentiles are used because healthy BMI changes a lot between ages 2 and 19.
Why can’t I use adult BMI categories for my teenager?
Because a BMI that is healthy at 17 can be high at 8. Adult cut-offs (25, 30) apply from age 20; until then, weight status comes from the percentile for the child’s age and sex.
Why does another calculator give a different percentile?
Three common reasons: it may still use the original 2000 method above the 95th percentile (CDC switched to extended percentiles in 2022, which are lower just above the 95th percentile and higher at very high BMIs); it may count the age differently (CDC uses completed months + 0.5, or the exact age in days); or it may use another reference, such as the WHO or IAP charts.
Which chart should I use for an Indian child?
The Indian Academy of Pediatrics recommends its 2015 charts for Indian children aged 5–18 (with overweight and obesity at the adult-equivalent BMI 23 and 27 lines) and the WHO standards under 5. This calculator uses the CDC charts, which are widely used internationally; ask your paediatrician which chart they follow.
What does class 2 or class 3 obesity mean?
They are the AAP’s grades of severe obesity: class 2 is a BMI of 120% to below 140% of the 95th percentile (or BMI 35 to below 40), class 3 is 140% or more (or BMI 40 or more), whichever threshold is lower. CDC uses “severe obesity” for 120% of the 95th percentile or a BMI of 35 or more.
Is my child’s information sent anywhere?
No. The calculation runs entirely in your browser — the age, height and weight never leave your device.