What Does Your Child’s BMI Mean for His or Her Health?

Medically Reviewed
a child standing on a scale
Talk with your son or daughter’s pediatrician to find out where he or she may fall on the scale.Sirinapa Wannapat/Getty Images; iStock

American children are increasingly tipping the scale, and the extra weight is 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 overweight or obese?

Doctors maintain that the way to tell involves a term you may already be familiar with: BMI, or body mass index.

What Is BMI, and Why Does Your Child’s Number Matter?

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, are considered obese, according to the Centers for Disease Control and Prevention (CDC). (1)

Childhood obesity is a pressing issue. Data from the CDC suggest that since the 1970s, childhood obesity has tripled. In 2015–2016, about 1 in 5 kids of school age in the United States were obese. (2)

“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 keeping tabs on their children’s nutrition and exercise habits.

What Are the Different Causes of Childhood Obesity?

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, since genetics and metabolism play a role in a child’s weight, past research shows. (3,4) Short sleep duration and community safety furthermore can affect a child’s risk. (3) But there are two factors that contribute to childhood obesity that you can control: eating habits and lack of exercise. (4)

While you may rely on convenient fast foods, processed foods, sodas, packaged snacks, candy, white breads and pastas, 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 the U.S. Department of Health and Human Services. (5) A diet high in unhealthy fat and sugar, and low in good-for-you nutrients — all of which characterizes these types of foods — can be a recipe for obesity, notes a study published in January 2015 in the British Journal of Nutrition. (6)

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. (4)

Your child also needs to get enough exercise to ward off unhealthy 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, according to the National Heart, Lung, and Blood Institute. (7)

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.

Parents in low-income communities often lack the education and resources needed to provide healthy meals. Children may visit corner stores to get unhealthy snacks or eat fast food because it’s more affordable, notes a study published in December 2015 in Childhood Obesity. (8) They may also spend more time indoors if the neighborhood isn’t safe for outdoor play, according to research cited in an article published in the April–June 2015 Journal of Family Medicine and Primary Care. (9)

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. Just like adults, children can struggle with stress, anxiety, and depression. If they aren’t taught healthy ways to cope with these feelings, they can develop an unhealthy relationship with food. (4)

What’s BMI Percentile? How Measuring Body Fat Is Different in Kids

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. (1)

The CDC recommends using BMI percentile to measure children and young people ages 2 years to 20. (10) Each time your child goes to the pediatrician, his or her height and weight is taken and the BMI percentile is plotted on a graph that compares your child’s number with those of other children the same age, height, and sex.

This is how to interpret the results, according to 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?

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. (1)

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. (1)

BMI Chart for Children by Age

BMI for children is sometimes referred to as “BMI-for-age,” because age is one factor that’s considered. As a child gets older, his or her 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. (1)

This chart compares a child’s BMI (calculated as weight in kilograms divided by height in meters squared) with his or her 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 Center children's hospital in New York City, recommends using online resources, like apps and calculators. For example, the CDC has an online BMI calculator that allows you to plug in a child’s age, sex, height, and weight.

You’ll need to take accurate height and weight measurements first. (11)

To measure your child’s height:

  1. Have your child take off shoes, hats, or hair accessories.
  2. Stand them on a flat floor against a flat wall with no floor molding.
  3. Make sure their legs are straight and their arms are at their sides with level shoulders.
  4. Have your child look straight ahead. Their line of sight should be parallel with the floor.
  5. Your child’s body (head, shoulders, butt, and heels) should be flat against the wall.
  6. 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.
  7. 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:

  1. Use a digital scale that’s placed on hard, even flooring.
  2. Have your child take off shoes and any heavy clothing, and stand with both feet in the center of the scale.
  3. 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. Whether you’re overweight or not, 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

You can measure your child’s body fat in other ways, but 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 measurements. (1)

They include:

  • Measuring skinfold thickness
  • Doing underwater weighing
  • Taking waist circumference
  • Using dual energy X-ray absorptiometry (DEXA) or a whole-body scan of bone and tissue

Although methods like DEXA and skinfold measurements are more accurate than BMI, BMI can provide a reasonably correct number to go by when these aren’t available, according to a study published in April 2016 in Public Health. (12)

One study published in July 2017 in JAMA Pediatrics suggests 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 more accurate in measuring body fat levels in children and teens ages 8 to 17 when compared with BMI. (13)

The Health Risks Associated With Childhood Obesity

When it comes to your child’s health, the earlier he or she 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. (4)

“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. (1,11)

Immediate potential health consequences of a high BMI percentile in children include: (1)

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 Mayo Clinic notes that the obesity epidemic has fueled a rise of type 2 diabetes diagnoses in children, and 40 percent of this group is asymptomatic. (14)

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. (9)

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. A policy statement by the American Academy of Pediatrics published in November 2017 in Pediatrics, suggests that these mental illnesses are associated with the stigma that obese or overweight adolescents can face. (15)

About 71 percent of teens seeking weight loss treatment reported being bullied about their weight within the past year, the statement reads. (15)

How to Make Healthy Changes to Your Child’s Diet and Lifestyle

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. (9) 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.

Kids generally eat what’s in the house, so stocking the pantry with healthy options can help them stay on track, according to a study published in January 2013 in the International Journal of Behavioral Nutrition and Physical Activity. (16)

Keep (17,18)

  • Fresh fruits and vegetables
  • Lean proteins, such as chicken, fish, and tofu
  • Whole grains, like brown rice and whole grain breads
  • Low-fat dairy

Ditch (17,18)

  • Packaged and processed snacks, including chips, cookies, cakes, and candy
  • Soft drinks and sugary juice

Increasing exercise time is also an important step. The CDC recommends children get at least 60 minutes of moderate to high-intensity physical activity each day. (19)

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.”

Additional reporting by Moira Lawler.

Editorial Sources and Fact-Checking

  1. About Child and Teen BMI. Centers for Disease Control and Prevention (CDC). May 15, 2015.
  2. Childhood Obesity Facts. CDC. January 29, 2018.
  3. Vos M, Welsh J. Childhood Obesity: Update on Predisposing Factors and Prevention Strategies. Current Gastroenterology Reports. August 12, 2010.
  4. Childhood Obesity Causes & Consequences. CDC. December 15, 2016.
  5. Research Brief Childhood Obesity. Office of the Assistant Secretary for Planning and Evaluation. March 1, 2005.
  6. Alkerwi A, Crichton G, Herbert J. Consumption of Ready-Made Meals and Increased Risk of Obesity: Findings From the Observation of Cardiovascular Risk Factors in Luxembourg Study. British Journal of Nutrition. January 28, 2015.
  7. Reduce Screen Time. National Heart, Lung, and Blood Institute. February 13, 2013.
  8. Rogers R, Eagle TF, Sheetz A, et al. The Relationship Between Childhood Obesity, Low Socioeconomic Status, and Race/Ethnicity: Lessons From Massachusetts. Childhood Obesity. December 11, 2015.
  9. Sahoo K, Sahoo B, Choudhury AK, et al. Childhood Obesity: Causes and Consequences. Journal of Family Medicine and Primary Care. April 2015.
  10. Child Obesity Facts. CDC. January 29, 2018.
  11. Measuring Children’s Height and Weight Accurately at Home. CDC. May 15, 2015.
  12. Jensen NS, Camargo TF, Bergamaschi DP. Comparison of Methods to Measure Body Fat in 7-to-10-Year-Old Children: A Systematic ReviewPublic Health. April 2016.
  13. Peterson C, Haiyan S, Thomas DM, et al. Tri-Ponderal Mass Index vs. Body Mass Index in Estimating Body Fat During Adolescence. Journal of American Medical Association. July 2017.
  14. Type 2 Diabetes in Children. Mayo Clinic. April 19, 2017.
  15. Pont S, Puhl R, Cook SR, Slusser W. Stigma Experienced by Children and Adolescents With Obesity. American Academy of Pediatrics. November 2017.
  16. Davison KK, Jurkowski JM, Kaigang L, et al. A Childhood Obesity Intervention Developed by Families for Families: Results from a Pilot Study. International Journal of Behavioral Nutrition and Physical Activity. January 5, 2013.
  17. Childhood Obesity. Mayo Clinic. November 17, 2016.
  18. Tips for Parents: Ideas to Help Children and Maintain a Healthy Weight. CDC. September 13, 2017.
  19. How Much Physical Activity Do Children Need? CDC. June 4, 2015.
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