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- For children and teens aged 2 to 19, BMI is compared with others of the same age and sex. The result is a BMI-for-age percentile, not an adult category.
- CDC categories: under the 5th percentile is underweight, 5th to under 85th is healthy weight, 85th to under 95th is overweight, and 95th or above is obesity.
- The calculator uses the CDC BMI-for-age growth charts, with the CDC 2022 extended method for very high BMIs.
- It is a screening tool, not a diagnosis. This page is general information, not medical advice.
How to use the BMI percentile calculator
Choose units and sex
Pick US units (feet, inches, pounds) or metric (centimeters, kilograms), then choose girl or boy. The growth charts are different for each.
Enter the age
Type the age in whole years and the extra months. Percentiles change quickly with age, so the months matter, especially in young children.
Enter height and weight
Use a recent, accurate measurement without shoes or heavy clothes.
Read the result
You get the BMI-for-age percentile, the CDC category, the healthy BMI and weight range for that age and height, the z-score and the steps used.
How BMI percentile is calculated
First the calculator works out BMI the same way as for adults: weight in kilograms divided by height in meters squared. It then compares that BMI with the CDC growth chart for the child’s sex and age in months, using the LMS values the CDC publishes for every half month from 2 to 20 years.
BMI percentile formulas
BMI = weight (kg) ÷ height (m)², or 703 × weight (lb) ÷ height (in)²
z-score = ((BMI ÷ M)L − 1) ÷ (L × S)
Percentile = the share of the normal curve below that z-score
At or above the 95th percentile: percentile = 90 + 10 × Φ((BMI − P95) ÷ sigma)
L, M and S are the CDC values for the child’s sex and age, P95 is the BMI at the 95th percentile and sigma is the CDC 2022 spread value used above it. Φ is the standard normal distribution.
A child is placed at the half-month point of their completed age, so 10 years and 0 months is read at 120.5 months on the chart. That is the same convention the CDC data files use, and the calculator interpolates between rows.
BMI categories for children and teens
CDC BMI-for-age categories
For ages 2 through 19, by percentile for age and sex.
- Below the 5th percentile Underweight
- 5th to under 85th Healthy weight
- 85th to under 95th Overweight
- 95th or above Obesity
- 120% of the 95th or more, or BMI 35+ Severe obesity
Doctors may use more detailed classes for severe obesity, and they look at growth over time, not one number.
What a BMI percentile means
A percentile compares a child with a large reference group of children of the same age and sex. A girl at the 60th percentile has a higher BMI than about 60% of girls her age in the CDC reference data. It is not a score to pass or fail, and the 50th percentile is not a target every child must reach.
The same BMI can land in a very different place at different ages, because body fat changes as children grow. A BMI of 23.3 is in the normal range for an adult but is above the 99th percentile for a 6-year-old boy. That is why adult BMI categories do not work for children.
Worked examples
Example 1: a 10-year-old girl
She is 10 years and 0 months old, 4 ft 7 in tall and weighs 70 lb.
- Age on the chart 120.5 months
- BMI 703 × 70 ÷ 55² = 16.3
- Percentile 39th
- Category Healthy weight
- Healthy weight for her height 60.4 lb to under 86.0 lb
Her BMI is higher than about 39% of girls her age in the CDC data.
Example 2: a 14-year-old boy
He is 14 years and 6 months old, 5 ft 5 in tall and weighs 150 lb.
- BMI 703 × 150 ÷ 65² = 25.0
- Percentile 92nd
- Category Overweight
- BMI as % of the 95th percentile 94.4%
- Healthy weight for his height 97.8 lb to under 138.6 lb
For a teen the percentile decides the category, not the adult cut-off of 25.
Example 3: a 6-year-old boy
He is 6 years and 0 months old, 3 ft 10 in tall and weighs 70 lb.
- BMI 703 × 70 ÷ 46² = 23.3
- Percentile 99.4th (extended method)
- BMI as % of the 95th percentile 126.3%
- Category Severe obesity
Above 120% of the 95th percentile, the CDC calls this severe obesity, even though 23.3 would be a normal BMI for an adult.
Example 4: metric units
A 15-year-old girl is 160 cm tall and weighs 45 kg.
- BMI 45 ÷ 1.60² = 17.6
- Percentile 17th
- Category Healthy weight
- Healthy weight for her height 41.8 kg to under 61.6 kg
The method is the same in either system of units.
Limits of BMI percentile
BMI cannot tell fat from muscle or bone, and children grow and go through puberty at different times. An athletic teen can have a high percentile with little extra fat. One measurement also says less than the trend across several checkups, which is how pediatricians use growth charts. The CDC charts are a US reference, and this calculator covers ages 2 to 19 only. For children under 2, doctors use the WHO growth charts instead.
Where a BMI percentile calculator helps
Before a checkup
Have a number ready to talk through with your pediatrician.
School and sports forms
Some forms ask for a BMI or BMI percentile.
Growth over time
Compare results from several checkups to see the trend.
Reading a doctor’s note
Understand what a percentile in a report means.
For anyone aged 18 and over, use the BMI calculator for adults. The height calculator estimates adult height from parents’ heights, and the calorie calculator estimates daily energy needs. A BMI percentile is general information, not medical advice. Please talk to your child’s doctor before making changes to how your child eats or exercises.
BMI percentile calculator FAQ
What is a BMI percentile?
It shows how a child’s BMI compares with children of the same age and sex in the CDC growth charts. The 75th percentile means the BMI is higher than about 75% of that group.
What is a healthy BMI percentile for a child?
For ages 2 to 19, the CDC treats the 5th to under the 85th percentile as healthy weight.
How is BMI percentile calculated?
BMI is worked out from height and weight, then turned into a z-score with the CDC L, M and S values for the child’s age and sex. The z-score gives the percentile. Above the 95th percentile, the CDC 2022 extended method is used.
Why can’t I use the adult BMI chart for my child?
Body fat changes with age and differs between girls and boys during growth, so a fixed adult cut-off would mislabel many children. Percentiles compare a child with others of the same age and sex.
What does the 95th percentile mean?
A BMI at or above the 95th percentile for age and sex is in the obesity range. At 120% of the 95th percentile or a BMI of 35 or more, the CDC calls it severe obesity.
Does this calculator use the CDC growth charts?
Yes. It uses the CDC BMI-for-age charts for ages 2 to 20 and the CDC 2022 extended BMI-for-age method for BMIs at or above the 95th percentile.
When should I switch to the adult BMI calculator?
The CDC child and teen charts cover ages 2 through 19, and the CDC uses adult categories from 20. Our adult BMI calculator follows the WHO, which applies adult categories from 18, so for 18 and 19 year olds both views can help.