Calculate BMI for children and teens aged 2 to 20 and see where it falls on the CDC BMI-for-age growth chart. Get the percentile, z-score, weight category, the healthy BMI and weight range for your child's age and height, and the full cutoff table.
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Sex
Age from
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in
lb
cm
kg
Enter your values to see the result.
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How to use the Child BMI Calculator
Choose units and sex.
Enter the age in years and months, or the birth date and the date measured.
Enter height and weight measured without shoes and in light clothing.
Read the percentile and category, plus the healthy weight range for this height.
Check the cutoff table to see 5th, 85th and 95th percentile BMI at each age.
How the child BMI percentile is calculated
BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)².
LMS parameters for the child's sex and age are looked up from the CDC 2000 BMI-for-age reference: L (skewness), M (median BMI) and S (coefficient of variation).
Z-score = ((BMI ÷ M)L − 1) ÷ (L × S).
Percentile = the standard normal cumulative probability of z × 100.
Example: a boy aged 8 years 6 months, 4 ft 3 in (129.5 cm) and 62 lb (28.1 kg) has a BMI of 16.8, which is around the 66th percentile: a healthy weight.
Weight status categories (CDC, ages 2–19)
Category
BMI-for-age percentile
Underweight
Less than the 5th percentile
Healthy weight
5th to less than the 85th percentile
Overweight
85th to less than the 95th percentile
Obesity
95th percentile or greater
Severe obesity (class 2)
BMI ≥ 120% of the 95th percentile
Severe obesity (class 3)
BMI ≥ 140% of the 95th percentile
95th percentile BMI by age (approximate, CDC)
Age
Boys 85th
Boys 95th
Girls 85th
Girls 95th
2
18.2
19.3
18.0
19.1
5
16.9
17.9
16.9
18.3
8
18.0
20.0
18.2
20.6
10
19.3
22.0
19.9
22.9
12
21.0
24.2
21.6
25.2
14
22.7
26.0
23.2
27.2
16
24.1
27.5
24.4
28.9
18
25.5
28.9
25.4
30.3
BMI percentile is a screening measure, not a diagnosis. A very muscular teen can have a high BMI without excess fat, and growth spurts can change percentiles quickly. Your child's doctor tracks the trend over time.
Frequently asked questions
Why do children need a BMI percentile instead of adult BMI categories?
Children's body fat changes as they grow and differs between boys and girls, so a single BMI number means different things at different ages. A BMI of 19 is in the healthy range for a 13-year-old boy but above the 95th percentile for a 5-year-old boy. Percentiles compare a child with others of the same age and sex.
What are the BMI percentile categories for children?
CDC categories for ages 2–19: underweight below the 5th percentile, healthy weight from the 5th to less than the 85th, overweight from the 85th to less than the 95th, and obesity at the 95th percentile or above. Severe obesity is a BMI at or above 120% of the 95th percentile (class 2), and 140% or more is class 3.
How is the BMI percentile calculated?
First BMI = weight (kg) ÷ height (m)². Then the CDC LMS method turns BMI into a z-score: z = ((BMI ÷ M)^L − 1) ÷ (L × S), where L, M and S are reference values for the child's age and sex. The percentile is the share of the normal distribution below that z-score.
How accurate is this calculator?
It uses CDC 2000 BMI-for-age reference values at each year of age, interpolated by month, so results normally match the CDC calculator to within about a percentile point. Percentiles above the 97th are less precise with the LMS method, which is why percent of the 95th percentile is shown. A pediatrician uses measured values and growth history to interpret the result.
What does the 50th percentile mean?
It means the child's BMI is higher than that of half of children of the same age and sex in the CDC reference population, and lower than the other half. It is the median, not a target; anything from the 5th to the 85th percentile counts as a healthy weight.
Can I use this for a child under 2?
No. BMI-for-age charts start at 2 years. For babies and toddlers under 2, doctors use WHO weight-for-length charts; try the baby percentile calculator.
Why did my child's percentile change when they grew taller?
Percentiles depend on age as well as height and weight. BMI naturally falls in early childhood, reaches a low point around ages 4 to 6 (adiposity rebound) and then rises through adolescence, so the same BMI can be a different percentile a year later.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.