Child and Teen BMI: A Complete Guide

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American children are increasingly tipping the scale, and the extra weight may be putting them at risk for immediate and future health complications, including depression, type 2 diabetes, and heart disease. But how do you know if your child is classified as overweight or obese? Medically speaking, doctors use a term you may already be familiar with: BMI, or body mass index.
What Is BMI, and Why Does Your Child’s Number Matter? Purpose BMI is a scale that defines obesity by taking body weight and height into account. Children whose weight puts them in the 95th percentile, or heavier than 95 percent of children their age according to a chart from 2000, are considered obese, according to the Centers for Disease Control and Prevention (CDC) . Data from the CDC suggests that since the 1970s, childhood obesity has more than tripled. In 2017–2018, about 1 in 5 kids of school age in the United States were obese. “Right now, the obesity epidemic is probably the worst it’s ever been,” says Daniel Ganjian, MD , a pediatric obesity specialist at Providence Saint John’s Health Center in Santa Monica, California. He recommends that all parents focus on prevention by encouraging healthy eating habits and regular physical activity.
What Are the Different Causes of Childhood Obesity? Causes Various factors may contribute to your child’s weight, including family history, mental health issues , socioeconomic status, and lifestyle habits. Some of these are within your control and others aren’t. Children with family members who are overweight or obese are more likely to struggle with weight issues, too, because genetics play a role in a child’s weight, as MedlinePlus notes. School and community safety furthermore can affect a child’s risk. But there are two factors that contribute to childhood obesity that you can control: eating habits and lack of exercise. While you may rely on convenient fast foods, baked goods, vending machine snacks, sweets, and sugary drinks to feed your child, it’s important to keep in mind that these eating choices can result in unhealthy weight gain, according to Mayo Clinic . Dr. Ganjian says eating at a restaurant or having fast food more than once a week and not eating fruits and vegetables can put you and your family at a greater risk for obesity. Your child also needs to get enough exercise to ward off excess weight gain. That can be tough in this day and age, when tablets, laptops, and gaming systems abound. But the more time children spend in front of screens, the less likely they are to get the exercise they need to burn off extra calories, per the National Heart, Lung, and Blood Institute . On the flip side, your socioeconomic status can affect your child’s risk of being overweight or obese, but is less controllable than other factors. People in low-income communities often lack safe places to exercise and have limited access to supermarkets, so they may be more likely to reach for unhealthy convenience foods like frozen meals, crackers, and cookies, per the Mayo Clinic. Working with your child’s pediatrician to identify healthy-eating and exercise strategies can help reduce their risk for childhood obesity. Your child’s weight can affect more than just their physical appearance, according to Mayo Clinic. Overweight children may face bullying and develop low self-esteem, anxiety, or depression.
What’s BMI Percentile? How Measuring Body Fat Is Different in Kids Percentile As an adult, you can calculate your BMI by taking your body weight in pounds and dividing that by the value of your height in inches squared, and then multiplying that value by 730. But because children and teens are still growing, their BMIs are plotted on a graph as percentiles. Each value is referred to as a BMI percentile, as the CDC notes. BMI percentile can be used to measure children and young people ages 2 to 20. Each time a child goes to the pediatrician, their height and weight are taken and their BMI percentile is plotted on a graph that compares their number with those of other children the same age, height, and sex. This is how to interpret the results, per the CDC: Underweight: less than 5th percentile Healthy weight: 5th percentile to less than 85th percentile Overweight: 85th percentile to less than 95th percentile Obese: equal to or greater than 95th percentile
What Is a Normal BMI Range for a Child? Ranges According to the CDC’s guidelines, a child’s BMI is considered healthy if it falls in between the 5th and 85th percentiles. Unlike with adults, there is no specific BMI number range to stay within, because a child’s BMI is presented as a percentile that takes weight, height, age, and sex into account. What BMI Is Considered Overweight for a Child? A child whose BMI falls between the 85th and 95th percentiles is considered overweight, while children at or above the 95th percentile (meaning their weight is higher than that of 95 percent of their peers) qualify as obese, per the CDC.
BMI Chart for Children by Age Chart Calculation BMI for children is sometimes referred to as “BMI-for-age,” because age is one factor that’s considered. As a child gets older, weight, height, and amount of body fat change, so the best practice is to compare children with other children of the same age and sex, per the CDC. A chart from the CDC (linked above) compares a child’s BMI (calculated as weight in kilograms divided by height in meters squared) with their age. The red portion is associated with childhood obesity. How to Calculate Your Child’s BMI Percentile on Your Own To calculate your child’s BMI percentile on your own, Marisa Censani, MD , a pediatric endocrinologist at New York-Presbyterian Komansky Children’s Hospital in New York City, recommends using online resources, like apps and calculators. For example, the CDC’s online BMI calculator allows you to plug in a child’s age, sex, height, and weight. You’ll need to take accurate height and weight measurements first, as the CDC notes. To measure your child’s height: Have your child take off shoes, hats, or hair accessories. Stand them on a flat floor against a flat wall with no floor molding. Make sure their legs are straight and their arms are at their sides with level shoulders. Have your child look straight ahead. Their line of sight should be parallel with the floor. Your child’s body (head, shoulders, butt, and heels) should be flat against the wall. Using a flat surface, such as a ruler or a piece of cardboard, make a right angle on the wall and lower the item until it reaches the top of the child’s head. Make a mark on the wall where the bottom of the flat surface touches the top of your child’s head. Then use a measuring tape to measure from the bottom of the floor to the mark. To measure your child’s weight: Use a digital scale that’s placed on hard, even flooring. Have your child take off shoes and any heavy clothing, and stand with both feet in the center of the scale. Record their weight as it appears on the scale to the nearest decimal point. Ganjian doesn’t advise waiting for BMI to get into the trouble zone before you make healthy lifestyle changes. Regardless of your weight, everyone in the household can benefit from eating nutritious food and exercising. “There are times when we’ll start an intervention before a kid gets to the 85th percentile because BMI is going up quickly,” he says.
Other Options for Measuring Your Child’s Body Fat Other Methods “As is true for adults, BMI can be a useful tool to assess whether a child’s weight puts them at risk for health problems, but further analysis is often needed,” says Linda Anegawa, MD , a Honolulu-based double board-certified physician in internal medicine and obesity medicine and medical director with PlushCare , a virtual health platform. You can measure your child’s body fat in other ways, though some of these approaches can only be done in a medical setting because of the tools they require. If your child’s BMI percentile is in the overweight or obese range, your doctor may recommend additional approaches, such as measuring skin-fold thickness and evaluating family history, diet, and physical activity, per the CDC. Although methods like dual energy X-ray absorptiometry (DEXA) and skin-fold measurements are more accurate than BMI, BMI can provide a reasonably correct number to go by when these aren’t available, according to a review . Another review suggested a formula called tri-ponderal mass index (TMI) may help accurately measure children’s BMI percentile. It’s calculated by weight divided by height cubed. Researchers found TMI to be a similar or superior way of measuring body fat levels in children and adolescents when compared with BMI.
The Health Risks Associated With Childhood Obesity Health Risks When it comes to your child’s health, the earlier a child learns to develop healthy eating and exercise patterns, the better. There are a variety of health risks that come from childhood obesity. Some may take years to show up, while others can be seen much earlier. If obesity continues into adulthood, the risk for health complications goes up, the CDC notes. “Children with a body mass index percentile at the 95th percentile [or above] have a greater chance of maintaining obesity into adulthood,” says Dr. Censani. Per the CDC, immediate potential health consequences of a high BMI percentile in children include: Prediabetes or Type 2 Diabetes If poor eating habits and weight gain are left unchecked, kids can develop prediabetes or type 2 diabetes at an early age. The obesity epidemic has fueled a rise of type 2 diabetes diagnoses in children, and 40 percent of this group is asymptomatic, according to Mayo Clinic . Sleep Apnea Sleep apnea causes breathing to stop and start irregularly during sleep. A BMI suggesting obesity puts children at a higher risk for developing the condition. If left untreated, sleep apnea can cause complications with the heart and lungs over time. Asthma Children with a BMI showing they’re overweight or obese are at a higher risk of developing asthma than children who have a normal BMI. Long-term potential health consequences of a high BMI percentile in children include: High Blood Pressure and High Cholesterol Both of these conditions develop over time and put you at risk for heart disease. Obesity during childhood can increase the likelihood of having heart problems later in life, per the CDC. Nonalcoholic Fatty Liver Disease When fatty deposits build up in the liver, it causes scarring that may eventually lead to liver damage. Cancer A diet that lacks proper nutrients and puts extra strain on the body may also increase your child’s risk of developing cancer. Arthritis Carrying extra weight puts pressure on the joints, which can lead to conditions like osteoarthritis over time. Three things factor in the development of these medical problems: age, genes, and weight, says Stephen Pont, MD, MPH , a pediatrician and the medical director for the Texas Center for the Prevention and Treatment of Childhood Obesity in Austin. The only one we can work on is weight, he says. In addition to physical health complications, children who are overweight or obese may also face mental health issues. They’re more likely to experience ailments such as depression, guilt, and anxiety, says Dr. Pont. What’s more, a review suggested that obese adolescents may also develop unhealthy eating behaviors, weight gain, and may have trouble with weight control as an adult.
How to Make Healthy Changes to Your Child’s Diet and Lifestyle Lowering BMI The good news is that, in most cases, the conditions listed above can be prevented or reversed once a child returns to a healthy weight. But it does take work, and often changes have to be made in the entire household. “If a child is a long way away from a healthy weight, it took them a while to get here, so we need to be patient,” says Pont. That means starting with small changes and gradually working your family up to a healthier diet and more exercise. Including children in that process helps them get invested and can improve the likelihood that healthy habits will stick. For example, you could ask them which healthy habits they want to work toward first and build from there. Consider offering nonfood rewards, like a trip or a new toy, for achieving the goals you set together. The focus should not be on weight loss, says Janet Lydecker, PhD , assistant professor of psychiatry at Yale School of Medicine in New Haven, Connecticut. That tends to be more harmful than helpful as kids are still growing and will continue to see the numbers on the scale rise, she says. Instead, “we encourage weight stability,” Dr. Lydecker says. “We want them to either have a flatter BMI growth curve or keep growing up but gain weight at a slower pace. That’s a big difference in how parents think about it because it’s so different than what we do for adults.” So rather than talking about weight, which can encourage eating disorders even when well intentioned, talk about desired outcomes and encourage healthy habits (as in: “We want your risk for diabetes to go down, so let’s eat a healthy dinner”), Lydecker says.Kids generally eat what’s in the house, so stocking the pantry with healthy options can help them stay on track. Per the CDC, you should keep: Fresh fruits and vegetables Lean meats, chicken, fish, lentils, and beans Lowfat or nonfat dairy And ditch: Packaged and processed snacks, including chips, cookies, crackers, and frozen meals Soft drinks and sugary juice, per the Mayo Clinic But avoid referring to the above as “junk food.” “We try to stay away from labeling food as bad or good and instead focus on a balanced diet,” says Lauren Salvatore, PsyD , assistant professor of psychiatry at Zucker School of Medicine at Hofstra-Northwell and director of the Eating Disorders Center for Northwell Health in Glen Oaks, New York. “If the parent labels certain foods as bad, it may have larger long-term implications.” Ganjian uses the 5-4-3-2-1-0 system, which stands for: 5 daily fruits and vegetables 4 compliments per day 3 portions of calcium per day No more than 2 hours in front of a screen daily (unless it’s homework related) 1 hour or more of exercise per day 0 sweet drinks (including juice) daily Another habit to change is how many meals the family is eating at restaurants or ordering out each week. Instead, focus on cooking healthy meals at home. When you’re preparing the food, you have control over the nutritional content. “The key is for families to support dietary changes for their children and to incorporate these changes for the entire family,” says Censani. “Encouraging and supporting children as they try new foods and helping prepare meals will give them a healthier approach to their dietary choices.” It’s also a good idea for parents to spend time with their child outside of the weight focus, such as by going on a date to the movies together. “It will show the kids that they are important and not just defined by their weight journey,” Dr. Salvatore says. That can go a long way in helping the child feel supported and comfortable enough to speak up about any difficult emotions they’re experiencing or bullying that may be taking place as a result of their weight. Lydecker suggests every parent have a regular check-in time with their child, whether that’s over breakfast, after school, or during family dinner. “If parents have that, then when something does come up they already have a process or system so it won’t feel like an extra big deal to sit the child down,” she says. “And if there’s a regular check-in, parents are more likely to notice small shifts in moods and behaviors.” Some things to pay attention to include a child trying to skip meals, requesting to eat alone, avoiding several types of food, or developing restrictive eating habits, says Eleyna Garcia, PhD , assistant professor of psychiatry and behavioral sciences at the University of Texas Medical Branch in Galveston, Texas. A therapist can also develop an individualized treatment plan and can work to build a child’s self confidence, set goals, and identify adults at the child’s school who can serve as an ally during the school day, Dr. Garcia says.

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