π§ Child BMI Percentile Calculator
CDC BMI-for-age percentile for ages 2 to 20.
Growth-chart screening only, not a diagnosis. Talk to your pediatrician about what the percentile means.
A child's BMI means nothing until you compare it to other kids the same age and sex. That is what this calculator does: it takes your child's BMI and places it on the CDC's BMI-for-age growth chart as a percentile. A 10-year-old boy at the 87th percentile has a higher BMI than 87 percent of boys his age, which lands him in the overweight band. The percentile, not the raw BMI number, is what pediatricians use.
How to Use This Calculator
Pick imperial or metric, choose boy or girl, and enter age, height, and weight. The calculator works out the BMI, then runs it through the CDC's LMS parameters for that exact age and sex to get the percentile.
Measure height without shoes, standing straight against a wall, and weight in light clothing on a reliable scale.
Enter the child's age in years. Halves are fine: 10.5 for ten and a half. The CDC charts cover ages 2 through 20.
Read the percentile and the CDC weight category. Under the 5th percentile is underweight, 5th to 85th is healthy, 85th to 95th is overweight, and 95th and up is obesity.
Track it over time rather than reacting to one reading. A child drifting upward across percentiles over a year matters more than a single high number. For the adult version, see our BMI calculator.
The CDC Method Behind the Number
Kids grow, so a fixed cutoff like the adult 25 or 30 would mislabel half of them. The CDC solved this with the LMS method: for every month of age from 2 to 20, for each sex, the CDC publishes three parameters (L for skew, M for the median, S for spread) fitted from national survey data. The z-score formula converts any BMI into standard deviations from the median, and the normal curve turns that into a percentile. This page embeds the actual CDC LMS values at each year of age and interpolates between them, so the math matches what a pediatrician's chart software computes.
The categories are percentile bands, not BMI numbers: underweight is below the 5th percentile, healthy weight is 5th to below 85th, overweight is 85th to below 95th, and obesity is 95th and above. In 2022 the CDC added extended growth charts for severe obesity above the 95th percentile, since the old curves flattened out there. If your child lands at or above the 99th percentile, the pediatrician will likely use those extended charts.
Worked Example
A 10-year-old boy, 55 inches tall, 85 pounds. BMI = 38.6 kg / (1.397 m)^2 = 19.8. The CDC parameters for a 10-year-old boy are L = -2.78, M = 16.60, S = 0.119. z = ((19.8/16.60)^-2.78 - 1) / (-2.78 x 0.119) = 1.17, which converts to the 87.6th percentile: overweight, just above the 85th percentile line. Now the same boy at 75 pounds: BMI = 17.4, z = 0.42, percentile about 66: healthy weight. Ten pounds moved him across a category line, which shows why regular tracking beats one-off worry.
What the Percentile Bands Mean in Practice
The healthy band is wide on purpose: anything from the 5th to the 85th percentile counts as healthy weight, because normal kids vary enormously. Landing at the 80th percentile is not "almost overweight" any more than landing at the 10th is "almost underweight." Pediatricians watch the trajectory: a child who has always tracked near the 75th percentile is following their own curve, while a child jumping from the 50th to the 85th in a year deserves a closer look at diet, activity, sleep, and screen time.
Two caveats worth knowing. First, BMI cannot see muscle, so a very athletic kid can read high without excess fat; the pediatrician checks this by eye, not by arguing with the chart. Second, puberty scrambles everything: early developers temporarily gain BMI faster than their peers, and the percentile usually settles as growth evens out. That is also why our teen BMI calculator exists, with guidance tuned for the adolescent years.
When to Talk to the Pediatrician
Bring the percentile to the next well-child visit if it sits outside the 5th to 85th band, or if it has shifted more than about 10 percentile points between visits. The doctor will look at growth history, family patterns, diet, activity, and sometimes labs before deciding anything needs to change. For kids in the overweight or obesity bands, the evidence-backed first step is family-based lifestyle change, not a diet: regular meals, water instead of sugary drinks, an hour of active play daily, and consistent sleep. If you are also tracking growth in height, our child height percentile calculator uses the same CDC method.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
Why do kids use percentiles instead of fixed BMI cutoffs like adults?
Because kids are growing. A BMI of 22 is overweight for an 8-year-old but healthy for a 16-year-old, so a single cutoff cannot work. The percentile compares the child to same-age, same-sex peers on the CDC growth chart, which automatically adjusts for normal growth. That is why pediatricians never quote a child's raw BMI without the percentile next to it.
What BMI percentile is considered overweight for a child?
The CDC bands: below the 5th percentile is underweight, 5th to below 85th is healthy weight, 85th to below 95th is overweight, and 95th and above is obesity. These are screening categories, not diagnoses. A child at the 86th percentile gets flagged for a conversation, not a verdict.
My child is at the 90th percentile. Should I put them on a diet?
No, not on your own. Restrictive dieting in children can harm growth and set up disordered eating. The evidence-backed approach is family-wide habit change: regular meals, water instead of sugary drinks, daily active play, limited recreational screen time, and consistent sleep. Bring the percentile trend to the pediatrician, who may check labs and refer to a dietitian if needed.
How accurate are CDC growth charts?
They are the US reference standard, built from national survey data on thousands of children and smoothed by CDC statisticians. They describe the population accurately. For one individual child they are a screening tool: they flag who needs a closer look, they do not diagnose anything by themselves.
Does the calculator work for children under 2?
No. Under age 2, pediatricians use WHO growth standards with weight-for-length charts, not BMI. The CDC BMI-for-age charts start at 24 months. If your toddler is under 2, ask the pediatrician to plot weight-for-length at the next visit.
Can a muscular child have a high BMI percentile without being overweight?
Yes. BMI cannot tell muscle from fat, and athletic kids who play a lot of sport can land in the overweight band while being perfectly lean. The percentile flags them for a look, and the pediatrician resolves it in about ten seconds by looking at the child. The chart is a net, not a label.
What is the CDC extended BMI chart?
In 2022 the CDC released extended BMI-for-age charts for children above the 95th percentile, because the old curves flattened out in severe obesity and could not distinguish a BMI at the 97th from one far beyond it. If your child is at or above the 99th percentile, ask the pediatrician to use the extended chart for tracking.
How often should I check my child's BMI percentile?
At each well-child visit is plenty, which is usually yearly after early childhood. Checking monthly at home creates anxiety without adding information, because normal growth wobbles. What matters is the trend across a year or more, not any single reading.
Do boys and girls use the same chart?
No, the CDC publishes separate LMS parameters for boys and girls, because growth timing and body composition differ by sex. This calculator picks the right table automatically when you select boy or girl.
My teen's percentile jumped during puberty. Is that normal?
Often yes. Early developers gain BMI faster than average during the growth spurt, and the percentile can spike for a year or two before settling. Late developers show the opposite pattern. The pediatrician reads the percentile alongside Tanner stage and growth velocity, not in isolation.