BMI for Kids: How BMI Percentiles Work (CDC Charts Explained)

You have probably seen a BMI chart for adults. Below 18.5 is underweight, 18.5 to 24.9 is healthy, 25 to 29.9 is overweight, and 30 and above is obesity. Those numbers are fixed, and they work the same way for every adult.

None of that applies to your child. BMI for kids does not use fixed cutoffs at all. A BMI of 22 can be perfectly healthy for a 15-year-old and a reason for concern in an 8-year-old. The number only means something when it is compared with other children of the same age and sex, and that comparison is called a BMI percentile.

This guide explains BMI for kids in plain language. You will learn how to calculate BMI for kids with the same simple formula adults use, how to read the percentile on the CDC growth chart, what each percentile band means, how to measure height and weight accurately at home, what to do at each band without shaming your child, and when a pediatrician should be involved.

What Is BMI for Kids?

BMI for kids starts with the same formula as adult BMI. You divide a child’s weight by their height squared. The result is a number like 15.2 or 17.9. So far, nothing is different.

The difference in BMI for kids is what happens next. For adults, that number goes into fixed bands. For children, the number is plotted on a CDC BMI-for-age growth chart, and it comes out as a percentile. A percentile tells you where your child’s BMI sits compared with other children of the same age and sex in the reference population.

Here is what a BMI for kids percentile means in practice. If your daughter is at the 70th percentile, her BMI is higher than the BMI of 70 percent of girls her age in the reference group, and lower than 30 percent of them. If your son is at the 28th percentile, his BMI is higher than 28 percent of boys his age, and lower than 72 percent of them.

The percentile is the whole point of BMI for kids. Children grow at very different rates, and body fat naturally rises and falls at different stages of development. A single fixed number cannot capture that. The BMI for kids percentile adjusts for age and sex, so a growing 6-year-old and a teenager going through puberty are each judged against children at the same stage.

The CDC BMI-for-age charts used for BMI for kids cover children and adolescents from ages 2 to 20. For children under 2, doctors use different charts based on weight for length, not BMI. From age 20 onward, the adult cutoffs apply.

How Is BMI for Kids Different From Adult BMI?

This is the single most important distinction in this guide, and it is the mistake most websites and calculators make. Adult BMI uses one set of numbers for everyone. BMI for kids uses percentiles that shift with age and sex.

Our guide on how to calculate BMI covers the adult method in full, with the fixed cutoffs of 18.5, 25, and 30. Do not apply those cutoffs when you check BMI for kids.

A real example shows the trap. A 9-year-old with a BMI of 19 falls in the adult “healthy” range, but on the CDC chart for 9-year-olds that same BMI lands near the 90th percentile, in the overweight band. Same number, different verdict. That is why the adult bands simply do not apply.

A real BMI for kids example shows why. An 8-year-old girl with a BMI of 22 falls above the 95th percentile on the CDC chart for her age and sex. That is the CDC category for obesity, and it deserves a pediatrician visit. A 15-year-old girl with the exact same BMI of 22 falls between the 50th and 75th percentile, which is comfortably in the healthy weight band. Same number, completely different meaning. Only the percentile tells you which one you are looking at.

The reason BMI for kids works this way is growth. Young children naturally carry a higher share of body fat, then lean out as they grow, then gain fat again around puberty, with boys and girls following different patterns. A fixed cutoff would flag normal development as a problem in one age group and miss real problems in another. Percentiles solve this by comparing each child only with peers at the same age and sex.

One more difference matters for BMI for kids. Adult BMI is often used on its own as a rough health marker. BMI for kids is a screening tool, and the American Academy of Pediatrics recommends that doctors check it at least once a year for every child age 2 and older. Screening means it flags children who may need a closer look. It does not diagnose anything by itself.

At What Age Does a Child Switch to Adult BMI?

At age 20, the adult BMI cutoffs take over: below 18.5 is underweight, 18.5 to 24.9 is healthy, 25 to 29.9 is overweight, and 30 or above is obesity. Between ages 2 and 20, BMI for kids is read as a percentile on the CDC charts. Under age 2, doctors use weight-for-length charts instead of BMI. If your teenager is close to 20, the pediatrician will tell you which chart applies at each visit.

How Do You Calculate BMI for a Child?

The BMI for kids formula is exactly the same as the adult one. Only the interpretation changes.

Metric formula: BMI = weight in kg / (height in meters x height in meters)

Imperial formula: BMI = (weight in lb / (height in inches x height in inches)) x 703

If you want the BMI for kids number without doing the math by hand, our BMI calculator runs the same formula instantly. But doing it once by hand shows you exactly where the number comes from, so let us work through three examples with every step shown.

Worked Example 1: Metric, a 10-Year-Old Boy

A 10-year-old boy weighs 35 kg and is 140 cm tall.

Step 1: Convert height to meters: 140 cm = 1.40 m.

Step 2: Square the height: 1.40 x 1.40 = 1.96.

Step 3: Divide weight by height squared: 35 / 1.96 = 17.86, which rounds to 17.9.

His BMI is 17.9. Plotted on the CDC BMI-for-age chart for 10-year-old boys, this falls in the healthy weight band, which runs from the 5th percentile to below the 85th percentile. The number 17.9 alone does not tell you that. The chart does.

Worked Example 2: Imperial, an 8-Year-Old Girl

An 8-year-old girl weighs 50 lb and is 48 inches tall.

Step 1: Square the height: 48 x 48 = 2,304.

Step 2: Divide weight by height squared: 50 / 2,304 = 0.0217.

Step 3: Multiply by 703: 0.0217 x 703 = 15.26, which rounds to 15.3.

Her BMI is 15.3. On the CDC chart for 8-year-old girls, this falls in the healthy weight band. Notice that her BMI is lower than the boy’s 17.9 in the first example, yet both are healthy. That is normal. Younger children typically have lower BMIs than older children, which is exactly why age matters.

Worked Example 3: The CDC’s Own Case, a 9-Year-Old Boy

The CDC publishes practice cases so parents and clinicians can check their method. One case is Sam, a 9-year-old boy who is 105.4 cm tall and weighs 16.9 kg.

Step 1: Convert height to meters: 105.4 cm = 1.054 m.

Step 2: Square the height: 1.054 x 1.054 = 1.111.

Step 3: Divide weight by height squared: 16.9 / 1.111 = 15.21, which rounds to 15.2.

His BMI is 15.2. The CDC places this at the 28th percentile for 9-year-old boys, which is in the healthy weight band. That means his BMI is higher than the BMI of 28 percent of boys his age in the reference population, and lower than 72 percent of them.

These three examples show the full workflow of BMI for kids: measure, calculate, then plot on the age and sex chart. The calculation is the easy part. The chart is where the meaning comes from.

How Do You Read a BMI Percentile?

In BMI for kids, a percentile is a ranking, not a score. A child at the 70th percentile did not get 70 percent on a test. It means their BMI is higher than 70 percent of children of the same age and sex in the CDC reference group. A child at the 50th percentile sits right in the middle. Half the reference group is higher, half is lower.

The CDC sorts BMI for kids percentiles into five bands. These are the only bands that matter for BMI for kids:

CDC Category	BMI-for-Age Percentile
Underweight	Below the 5th percentile
Healthy weight	5th percentile to below the 85th percentile
Overweight	85th percentile to below the 95th percentile
Obesity	95th percentile or above
Severe obesity	120% of the 95th percentile or above, or a BMI of 35 or above

A few honest notes about these BMI for kids labels. First, the words are CDC category names for a measurement. They describe where a number falls on a chart. They do not describe a child, and they say nothing about effort, habits, or worth. Second, the bands are screening cutoffs, not diagnoses. A child in the overweight band is not automatically unhealthy, and a child in the healthy band is not automatically healthy. The percentile is a prompt for a conversation, not a verdict.

Behind the scenes, the CDC converts a BMI for kids measurement into a percentile with a statistical method called the LMS method, which accounts for the fact that BMI is not spread evenly across children. You do not need to do that math yourself. The CDC’s child and teen BMI calculator does it for you, and your pediatrician’s office uses the same charts. The CDC explains how to plot and interpret these charts step by step in its plotting and interpreting guide.

If you use a chart on paper, the method is simple. Find your child’s age on the horizontal axis and their BMI on the vertical axis. Mark where the two meet. The curved line nearest that point tells you the percentile. The CDC publishes separate charts for boys and girls, so make sure you use the right one.

For very high BMI for kids readings, the CDC released extended BMI-for-age charts in 2022. The original 2000 charts are used when a BMI is at or below the 95th percentile, and the extended charts are used when it is above the 97th percentile. Either chart works in between. This matters mostly for clinicians tracking children with obesity, because the extended charts give more precise percentiles above the 95th line instead of bunching everyone together at the top.

How Do You Measure Your Child’s Height and Weight at Home?

A BMI for kids percentile is only as accurate as the two numbers behind it. A small measuring error can move a child across a band, especially near the 85th or 95th lines. These steps keep home measurements trustworthy.

Measuring Weight

Weigh your child first thing in the morning, after using the bathroom, before eating, wearing light clothing and no shoes. Use a digital bathroom scale on a hard, flat floor, not on carpet, which can add or subtract pounds. Have your child stand still in the center of the scale with weight even on both feet. Write the number down right away. Weigh twice and use the average if the two readings differ.

Weigh on the same scale each time. Different scales can disagree by a pound or more, and switching scales between check-ins creates fake changes. If your scale sits on carpet or wobbles, fix that before you trust the number.

Measuring Height

Height is where most home errors happen, because children squirm and walls are rarely perfect. Use a flat wall with no baseboard if you can, or a door frame. Have your child stand barefoot with heels, buttocks, shoulders, and the back of the head touching the wall, feet together, looking straight ahead with eyes level. Place a flat object like a hardcover book on top of the head, level with the wall, and mark the underside of the book. Measure from the floor to the mark with a tape measure.

Measure in the morning if you can. People are slightly taller in the morning than in the evening because the spine compresses during the day, and children are no exception. The difference is small, usually under a centimeter, but measuring at the same time of day keeps check-ins comparable.

How Often Should You Measure?

For BMI for kids tracking, measuring every 3 to 6 months is plenty, and it matches the pace of well-child visits. Measuring every week creates noise. Children grow in spurts, and a single week tells you almost nothing. What matters is the pattern across months: is the percentile roughly steady, drifting up, or drifting down?

Keep a simple BMI for kids log: date, height, weight, BMI, and percentile. One line per check-in is enough. Over a year, that log shows the trend, and the trend is what your pediatrician actually uses. A single reading can be thrown off by a growth spurt, a heavy meal, or a measuring slip. A trend across four or five readings is hard to fake.

What Does Each BMI Percentile Band Mean?

Underweight: Below the 5th Percentile

A child below the 5th percentile on a BMI for kids chart weighs less than 95 percent of children of the same age and sex in the reference group. This can be completely normal for a naturally slim child who has always tracked along a low percentile and is otherwise thriving. It can also signal that a child is not getting enough nutrition, has an illness that affects appetite or absorption, or is going through a growth spurt where height outran weight.

What to do: book a pediatrician visit. Do not try to “fatten up” a child with junk food, and do not restrict anything. The pediatrician will look for causes, check growth history, and advise on nutrient-dense meals if extra calories are needed. If your child has always been near the 3rd or 4th percentile and is active, eating well, and developing normally, the pediatrician may simply keep watching.

Healthy Weight: 5th Percentile to Below the 85th Percentile

This is the wide middle band where most children fall on a BMI for kids chart. A child here is growing in line with peers. The job is maintenance: keep offering balanced meals, keep active play part of every day, protect sleep, and keep measuring every few months.

What to do: stay the course. There is nothing to fix. The healthiest thing you can do at this band is to avoid turning food and weight into a source of stress. Children in this band still benefit from the same healthy routines as every other child, and they still need annual BMI screening, because percentiles drift as children grow.

Overweight: 85th Percentile to Below the 95th Percentile

A child in this BMI for kids band is heavier than 85 percent of peers of the same age and sex. This is the band where early, gentle action matters most, because habits set here often decide which direction the percentile moves next.

What to do: start with the whole family’s routines, not with the child. Swap sugary drinks for water, keep regular mealtimes, add active play, and protect sleep. Bring it up at the next well-child visit, or book one sooner if the percentile is climbing quickly. Do not put a child on a diet, do not comment on their body, and do not single them out with different food from the rest of the family. The goal at this band is usually to slow weight gain while height catches up, not to make a child lose weight.

Obesity: 95th Percentile or Above

A child at or above the 95th percentile on a BMI for kids chart is in the CDC category for obesity. This band deserves a pediatrician visit, not because the number itself is an emergency, but because the pediatrician needs to check for related health issues and help the family build a plan.

What to do: book a pediatrician visit. The visit usually includes height, weight, BMI percentile, growth chart review, blood pressure, family history, a food and activity history, a sleep review, and sometimes blood tests for cholesterol, blood sugar, or liver health. The pediatrician may refer the family to a structured program. The American Academy of Pediatrics supports family-based programs with regular contact over several months for children with obesity, and these programs work on nutrition, activity, and behavior skills together, with parents involved throughout.

Severe Obesity: 120% of the 95th Percentile or Above, or BMI 35 or Above

This is a subset of the BMI for kids obesity band for very high BMIs. The American Academy of Pediatrics further splits it into Class 2 obesity (120% to below 140% of the 95th percentile, or BMI 35 to below 40) and Class 3 obesity (140% of the 95th percentile or above, or BMI 40 or above).

What to do: see a pediatrician promptly. Children in this band need a full medical evaluation and a coordinated care plan, which may include specialist referrals. The same rule still applies: no diets, no shaming, no home weight-loss plans. This is medical care, and it belongs with the pediatrician and their team.

What Should You Do If Your Child Is in the Overweight or Obesity Band?

First, take a breath. A percentile is a screening result, not a report card on your parenting and not a prediction about your child’s future. Many children move between BMI for kids bands as they grow, especially around growth spurts and puberty. What matters is what happens next, and the next steps are calmer and simpler than most parents expect.

Change the household, not the child. The strongest evidence-backed approach is family-based. Everyone eats the same meals. Everyone gets active. Nobody gets a “special diet” while the rest of the family eats differently. Singling a child out teaches them that something is wrong with them. Changing the household teaches them that healthy habits are just what the family does.

Focus on behaviors, not on the number. The behaviors that move a percentile in the right direction are the same ones that help every child: water instead of sugary drinks, regular meals with vegetables and protein, fruit instead of sweets for snacks most of the time, at least 60 minutes of active play a day, limited recreational screen time, and enough sleep. Notice that none of these involve counting a child’s calories or weighing their food.

Let height do some of the work. For many children, especially younger ones, the pediatrician’s goal is not weight loss at all. It is weight maintenance while height increases. A child who holds the same weight for a year while growing 5 cm will see their percentile fall on its own. That is a normal, healthy path, and it is why doctors rarely aim for weight loss in growing children.

Work with the pediatrician, not around them. If the percentile is high or climbing, the pediatrician may suggest a structured family program. These programs typically involve regular sessions over several months, covering nutrition, activity, sleep, and behavior skills, with parents doing the work alongside the child. For children age 6 and older with obesity, programs with at least 26 hours of contact over several months have the strongest evidence behind them.

Protect your child’s relationship with food and with you. Do not comment on your child’s body, do not praise weight loss, do not ban foods outright, and do not use food as a reward or punishment. Research and clinical experience both point the same way: shame and restriction backfire. They raise anxiety, encourage secret eating, and damage the trust a child needs to accept help. The goal is a child who eats well, moves happily, and feels safe at home, not a child who is afraid of the scale.

Should I Put My Child on a Diet If Their BMI Percentile Is High?

No. Do not put a child on a weight-loss diet, calorie restriction, or any special eating plan without a pediatrician. Children are growing, and their bodies need steady nutrition. The pediatrician’s usual approach is to change family-wide routines first: water instead of sugary drinks, regular meals, more active play, less screen time, and better sleep. For many children, holding weight steady while height increases brings the percentile down on its own. Any plan that goes beyond normal healthy routines belongs with the pediatrician.

What Should You Do If Your Child Is Underweight?

A low BMI for kids percentile raises a different set of questions, and it deserves the same calm, pediatrician-led approach. Some children are naturally slim and have tracked along a low percentile since toddlerhood. If your child is active, eating a varied diet, meeting developmental milestones, and following their own steady curve, a low percentile may simply be their normal.

The pediatrician’s job is to sort that out. They will look at the growth history, check for illness, appetite problems, food intolerances, or conditions that affect absorption, and ask about mealtime behavior. If extra calories are needed, they will advise on nutrient-dense foods and regular meal and snack times.

What you should not do is force-feed, turn meals into battles, or load a child up with junk food and milkshakes. Pressure at the table makes eating worse, not better. Offer regular meals and snacks, keep mealtimes calm and screen-free, and let the pediatrician guide any nutrition changes. If your child is losing weight, refusing food, vomiting, or has symptoms like fatigue or stomach pain, do not wait for the next routine visit. Book one now.

When Should You See a Pediatrician?

The American Academy of Pediatrics recommends annual BMI for kids screening for every child age 2 and older, which usually happens at the well-child visit. Between visits, book an appointment sooner if you notice any of these:

• The percentile jumps across two or more major percentile lines between check-ins, in either direction.
• The percentile climbs steadily at every check-in, even if it is still in the healthy band.
• The percentile falls steadily, or your child is losing weight.
• Your child snores loudly or has pauses in breathing during sleep.
• Your child has unusual thirst, frequent urination, or dark, velvety skin patches around the neck or armpits.
• Your child has joint pain, especially in the hips or knees.
• Your child is being teased or bullied about weight, or seems anxious, withdrawn, or secretive about food.
• You are unsure how to talk about the result, or you feel the urge to put your child on a diet.

Bring your BMI for kids measurement log to the visit. Dates, heights, weights, BMIs, and percentiles give the pediatrician the trend, which is far more useful than a single reading. Also bring a short note about meals, activity, sleep, and screens, because those are the first things the pediatrician will ask about.

One more point worth making clearly: do not start any weight-loss plan, calorie restriction, supplement, or special diet for your child without a pediatrician. Children are growing, and their nutrition needs are different from adults. A plan that would be reasonable for an adult can harm a growing child. The pediatrician is the gatekeeper for every food or activity change that goes beyond normal healthy routines.

What If My Child’s BMI Percentile Keeps Going Up?

A steadily rising percentile deserves a pediatrician visit, even if it is still inside the healthy band. A jump across two or more major percentile lines between check-ins is a common reason doctors take a closer look. Bring your measurement log, and note any changes in meals, activity, sleep, screens, medications, or stress. The pediatrician will check for medical causes and help the family adjust routines. Do not start a diet or restriction plan on your own while you wait for the visit.

How Can You Talk to Your Child About BMI Without Harming Them?

How you talk about BMI for kids matters as much as what you do. Children remember weight comments for years, and a careless sentence can do more damage than a percentile ever will.

Do not use labels on your child. Words like overweight, obese, and fat do not belong in conversations with children, even when they appear on a chart. If your child asks what the doctor said, say something like: “The doctor checked how you are growing compared with other kids your age, and we are going to help your body grow strong with good food and play.” That is honest, and it keeps the focus on health, not on appearance.

Talk about behaviors, never about bodies. Say “let us drink water instead of soda because it helps our energy” rather than “you need to lose weight.” Say “let us walk to the park because it is fun” rather than “you need exercise.” Children respond to what is fun, tasty, and social. They shut down when they feel judged.

Never praise weight loss in a child. A child who hears “you look so much thinner” learns that their value is tied to their size. Praise effort instead: “you tried a new vegetable,” “you rode your bike for a whole hour,” “you slept well all week.” Those are the behaviors that actually matter.

Keep the whole family on the same plan. If the family eats the same food and does the same activities, no child feels singled out. If siblings get different rules, the child with the higher percentile learns that the problem is them. Family-wide habits protect every child in the house, including the ones whose percentiles look fine.

Watch for signs that the conversation is hurting. If your child starts skipping meals, hiding food, exercising in secret, weighing themselves constantly, or talking about their body with disgust, stop and talk to the pediatrician. Those are warning signs of disordered eating, and they need professional attention, not more willpower talk.

What Are the Limits of BMI for Kids?

BMI for kids is a useful screening tool, and it is also an imperfect one. Knowing its limits keeps you from overreacting to a single number.

It does not measure body fat directly. A BMI for kids number uses only height and weight. A muscular, athletic child can have a high BMI without excess body fat, because muscle is heavy. A child with low muscle mass can have a normal BMI while carrying more body fat than is healthy. The percentile flags children who may need a closer look. It does not measure what their bodies are made of.

Puberty timing changes everything. Two children of the same age can be at very different stages of puberty, and their BMIs will differ for that reason alone. Early developers often have higher BMIs than late developers of the same age. The percentile chart compares by age, not by puberty stage, so a child going through early puberty can look high on the chart while developing normally.

Growth is not a straight line. Children grow in spurts. Weight often jumps before height does, which temporarily pushes the BMI for kids percentile up, and then height catches up and the percentile falls again. A single high reading during a growth spurt is not a trend. That is why the pattern across several check-ins matters more than any one reading.

The reference population is historical. The CDC charts are built from survey data collected from American children over several decades. Populations change, and no reference group matches every child. Children of different ethnic backgrounds can have different typical body compositions, which is one more reason the percentile is a starting point for a conversation, not a final answer.

It says nothing about health by itself. A percentile does not measure blood pressure, blood sugar, cholesterol, fitness, sleep, mood, or diet quality. Two children at the same percentile can have very different health profiles. The pediatrician reads the percentile alongside all of those, which is why a visit matters more than a calculator result.

What Does a Healthy Daily Routine Look Like?

You do not need a complicated plan to support healthy growth. The routine below is the practical version of everything in this guide, and it works for children in every percentile band.

Meals: Three regular meals and one or two planned snacks, eaten at roughly the same times each day, mostly at the table and without screens. Build meals around vegetables, fruit, whole grains, and protein: eggs, chicken, fish, beans, lentils, yogurt, or cheese. Keep portions child-sized, and let your child decide when they are full. Forcing a child to finish a plate teaches them to ignore their own fullness signals.

Drinks: Water is the default. Milk with meals is fine for most children. Sugary drinks, including soda, sweetened juice, and sports drinks, are the single easiest win in a child’s diet, because they add a lot of calories and sugar without filling anyone up. Cutting them out often moves a percentile more than any other single change.

Activity: At least 60 minutes of physical activity a day for school-age children. It does not have to be organized sport. Walking, cycling, swimming, playground play, dancing, and active games all count. Break it up if needed. Three 20-minute bursts are as good as one hour. The best activity is the one your child will actually do again tomorrow.

Screens: Keep recreational screen time limited, and keep screens out of bedrooms and mealtimes. Screen time matters for weight in two ways: it replaces active time, and it encourages mindless snacking. A simple rule is no screens during meals, and a fixed daily limit the whole family follows.

Sleep: School-age children need roughly 9 to 12 hours of sleep a night, and teenagers need roughly 8 to 10 hours. Short sleep raises appetite hormones and pushes children toward sugary, high-calorie food the next day. A regular bedtime, a dark room, and no screens for the last hour before bed are the basics that work.

Check-ins: Measure height and weight every 3 to 6 months, calculate BMI for kids with the formula above, and note the percentile. Bring the log to every well-child visit. If the percentile is steady and your child is active and eating well, you are doing it right, whatever the exact number is.

Frequently Asked Questions