acalculator

BMI calculator: kids and teens 2 to 19

Enter your child’s sex, age, height and weight to see their BMI, where it falls on the CDC BMI-for-age chart, and the CDC weight category for children and teens.

Your numbers

Units
Sex
Based on
Weight category
Healthy weight

At 10 years, a BMI of 16.3 is at percentile 42.6: Healthy weight.

Healthy weight

  1. Underweight
  2. Healthy weight
  3. Overweight
  4. Obesity
BMI
16.3
BMI-for-age percentile
42.6
Z-score
-0.19
Share of the 95th percentile
73.6%
Healthy weight from
61.1 lb
Healthy weight up to
83.3 lb
Age
10 years

Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.

Weight category: Healthy weight. At 10 years, a BMI of 16.3 is at percentile 42.6: Healthy weight.

Where does this BMI-for-age percentile fall?

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Works out a child’s or teen’s BMI, its BMI-for-age percentile on the CDC growth charts (with the CDC extended method above the 95th percentile) and the CDC weight category, for ages 2 to 19.

Example with the default inputs (Sex Boy, Based on Age, Years 10, Months 0, Height 4 ft 7 in, Weight 70 lb) on the example date Wednesday, September 30, 2026: At 10 years, a BMI of 16.3 is at percentile 42.6: Healthy weight.

Method: BMI = weight ÷ height²; at or below the 95th percentile BMI (P95), z = ((BMI ÷ M)^L − 1) ÷ (L × S) and percentile = Φ(z) × 100; above P95, percentile = 90 + 10 × Φ((BMI − P95) ÷ sigma) and z = Φ⁻¹(percentile ÷ 100) (CDC extended BMI-for-age charts).

  • L, M and S come from the CDC 2000 BMI-for-age table for the sex, read on a straight line between table ages; P95 is the BMI at z = 1.6449; sigma comes from the CDC regression on age in years.
  • Age in months is 12 × years + months, or the days from birth to the measurement ÷ 30.4375. The categories are for ages 2 through 19.
  • Categories are read from the percentile rounded half up to one decimal place. Severe obesity: BMI at least 120% of P95 (one decimal place) or a BMI of 35.0 or more.
  • BMI is a screening measure for children. It does not measure body fat and is not a diagnosis.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Sex Girl, Based on Age, Years 9, Months 6.5, Height 4 ft 7.1 in, Weight 91.61 lb gives BMI 21.2, Z-score 1.421501, BMI-for-age percentile 92.2, Weight category Overweight, Share of the 95th percentile 94.7%.Source: CDC, Extended BMI-for-age growth charts data files: girl, 114.5 months, BMI 21.2, z = 1.4215, percentile 92.2 (L −2.257782149, M 16.57626713, S 0.132796819)
  2. Sex Boy, Based on Age, Years 4, Months 2.5, Height 3 ft 3.4 in, Weight 49.82 lb gives BMI 22.6, Z-score 2.831446, BMI-for-age percentile 99.8, Share of the 95th percentile 126.8%, Weight category Severe obesity.Source: CDC, Extended BMI-for-age growth charts data files: boy, 50.5 months, BMI 22.6, P95 17.8219, sigma 2.398288, percentile 99.7683, z 2.83
  3. Sex Girl, Based on Age, Years 12, Months 0, Height 5 ft 0 in, Weight 136 lb gives BMI 26.6, BMI-for-age percentile 96, Weight category Obesity.Source: CDC, Child and Teen BMI Categories: a 12-year-old girl, 5 feet, 136 pounds, BMI 26.6, 96th percentile, obesity
  4. Sex Girl, Based on Age, Years 6, Months 0.5, Height 3 ft 9.3 in, Weight 37.48 lb gives BMI 12.9, BMI-for-age percentile 0.8, Weight category Underweight, Z-score -2.390365.Source: CDC bmiagerev.csv, girls, 72.5 months
  5. Sex Boy, Based on Age, Years 19, Months 0, Height 5 ft 10.9 in, Weight 250 lb gives BMI 35, BMI-for-age percentile 97.8, Share of the 95th percentile 117.9%, Z-score 2.008654, Weight category Severe obesity.Source: CDC Child and Teen BMI Categories (severe obesity: 120% of P95, or a BMI of 35 or more); CDC bmiagerev.csv, boys, 228 months

How it works

1. Age in months. Enter the age as years and months (months may have decimals), or as a birth date and a measurement date:

  • age in months = 12 × years + months, or
  • age in months = (measurement date − birth date, in days) ÷ 30.4375.

The categories are for ages 2 through 19, so the age must be from 24 months up to, but not including, 240 months. Otherwise there is no answer (and no answer if the measurement date is before the birth date).

2. BMI = weight in kg ÷ (height in m)². The percentile uses this unrounded BMI. The BMI row shows it rounded half up to one decimal place.

3. L, M and S come from the CDC 2000 BMI-for-age table (bmiagerev.csv), used exactly as published. Its rows are at 24 months, then at 24.5, 25.5 and so on up to 239.5, then at 240 and 240.5 months. At a table age the row is used as it is; between two table ages a₀ < a < a₁, each of L, M and S is read on a straight line: L = L₀ + (a − a₀) ÷ (a₁ − a₀) × (L₁ − L₀), and the same for M and S.

4. The 95th percentile BMI at the age: P95 = M × (1 + L × S × z₉₅)^(1/L), where z₉₅ = Φ⁻¹(0.95), the exact inverse normal value 1.6448536269514727… (the engine uses the nearest double, 1.6448536269514729).

5. Percentile and z-score (the CDC extended BMI-for-age method):

  • If BMI ≤ P95: z = ((BMI ÷ M)^L − 1) ÷ (L × S), and percentile = Φ(z) × 100.
  • If BMI > P95: percentile = 90 + 10 × Φ((BMI − P95) ÷ σ), and z = Φ⁻¹(percentile ÷ 100). The calculator works out the upper tail directly, 1 − percentile ÷ 100 = Φ(−(BMI − P95) ÷ σ) ÷ 10, so it stays exact far above the 95th percentile. If that tail is 0 in floating point, there is no answer.
  • σ (sigma) from the CDC regression on age in years (age in months ÷ 12): boys σ = 0.3728 + 0.5196 × age − 0.0091 × age²; girls σ = 0.8334 + 0.3712 × age − 0.0011 × age².

Φ is the standard normal cumulative distribution. The percentile is rounded half up to one decimal place and then shown between 0.1 and 99.9. The z-score is shown to two decimal places.

6. The category is read from the percentile rounded half up to one decimal place (before the 0.1 to 99.9 limit): below 5.0 underweight; 5.0 to below 85.0 healthy weight; 85.0 to below 95.0 overweight; 95.0 or more obesity. It is severe obesity instead when the share of the 95th percentile, BMI ÷ P95 × 100 rounded half up to one decimal place, is 120.0 or more, or when the BMI rounded half up to one decimal place is 35.0 or more.

7. Healthy weight range at this height. The weights whose percentile shows as 5.0 to 84.9 are those from the BMI at percentile 4.95 up to just under the BMI at percentile 84.95. So: from M × (1 + L × S × Φ⁻¹(0.0495))^(1/L) × height², up to M × (1 + L × S × Φ⁻¹(0.8495))^(1/L) × height².

Rounding. Every “rounded half up” on this page reads the decimal value: a result within 1e-9 (relative) of a half counts as the half. For example, 80 ÷ 1.6², which a computer stores as 31.249999999999993, rounds to 31.3.

Assumptions

  • At or below P95, Φ is computed with Marsaglia’s series (J Stat Softw 2004), within 5e-15 of the exact value.
  • The CDC 2000 charts describe US children measured from 1963 to 1994; the extended method changes only percentiles above the 95th.
  • Measure height without shoes and weight in light clothes.
  • This calculator gives general information. It is not medical advice or a diagnosis; talk to your child’s doctor about their weight.

Worked examples by hand

The CDC’s example: a girl of 9 years 6 months (114.5 months) with a BMI of 21.2 (1.40 m and 41.552 kg). The table row for girls at 114.5 months is L = −2.257782149, M = 16.57626713, S = 0.132796819. P95 = 16.57626713 × (1 − 2.257782149 × 0.132796819 × z₉₅)^(−1 ÷ 2.257782149) = 22.3979, so her BMI is below it. z = ((21.2 ÷ 16.57626713)^−2.257782149 − 1) ÷ (−2.257782149 × 0.132796819) = 1.4215, and the percentile is Φ(1.4215) × 100 = 92.2: overweight. Her BMI is 21.2 ÷ 22.3979 = 94.7% of the 95th percentile.

The CDC’s example above the 95th percentile: a boy of 4 years 2 months (50.5 months) with a BMI of 22.6 (1 m and 22.6 kg). P95 = 17.8219 and σ = 0.3728 + 0.5196 × 4.2083 − 0.0091 × 4.2083² = 2.3983. Percentile = 90 + 10 × Φ((22.6 − 17.8219) ÷ 2.3983) = 90 + 10 × Φ(1.9923) = 99.7683, shown as 99.8, and z = Φ⁻¹(0.997683) = 2.83. BMI ÷ P95 = 126.8%, which is 120% or more: severe obesity.

The CDC’s example: a 12-year-old girl, 5 ft tall and 136 lb. BMI = 61.689 kg ÷ 1.524² = 26.56, shown as 26.6. At exactly 12 years (144 months) the percentile is 96.0: obesity, and 105.4% of the 95th percentile, so not severe.

A boy of 19 years (228 months), 1.80 m and 113.4 kg. BMI = 113.4 ÷ 3.24 = 35.0. P95 at 228 months is 29.69, so the BMI is above it: percentile = 90 + 10 × Φ((35.0 − 29.69) ÷ σ) with σ = 0.3728 + 0.5196 × 19 − 0.0091 × 19² = 6.9601, giving 97.8 (z = 2.01). BMI ÷ P95 = 117.9%, under 120%, but the BMI is 35.0 or more, so the category is severe obesity.

A girl of 6 years 0.5 months (72.5 months), 1.15 m and 17 kg. BMI = 17 ÷ 1.3225 = 12.85, shown as 12.9. With L = −3.225606516, M = 15.21690296, S = 0.093803033, z = ((12.854 ÷ 15.2169)^−3.2256 − 1) ÷ (−3.2256 × 0.093803) = −2.39, and the percentile is 0.8: underweight.

Other questions people ask

Why is BMI different for children?

Body fat changes a lot as children grow, and differs between boys and girls. So a child’s BMI is compared with other children of the same sex and age, as a percentile, instead of with fixed adult cut-offs such as 25 and 30.

What are the BMI categories for children?

The CDC uses the BMI-for-age percentile: underweight below the 5th percentile, healthy weight from the 5th to below the 85th, overweight from the 85th to below the 95th, and obesity at the 95th or above. Severe obesity is a BMI of 120% of the 95th percentile or more, or a BMI of 35 or more.

What is the extended BMI-for-age method?

The 2000 CDC charts are not reliable far above the 95th percentile. In 2022 the CDC published extended charts that use a different method there (Wei and others, 2020): above the 95th percentile, the percentile is 90 + 10 × Φ((BMI − P95) ÷ σ). Below the 95th percentile nothing changes. This calculator uses the extended method above the 95th percentile.

What does "percent of the 95th percentile" mean?

It is the child’s BMI divided by the 95th percentile BMI for the age and sex. A value of 120% or more is the CDC’s severe obesity cut-off, and the American Academy of Pediatrics splits severe obesity into class 2 (120% to under 140%) and class 3 (140% or more).

At what age should I use the adult BMI calculator instead?

From the 20th birthday. The CDC child and teen categories are for ages 2 through 19. Under 2, doctors use weight-for-length on the WHO charts instead of BMI.

Is BMI a good measure for my child?

BMI is a screening measure. It does not measure body fat directly, and muscular or tall children can have a high BMI. A pediatrician looks at BMI with growth over time, family history and other checks.