Child and Teen Body Mass Index (BMI): A Complete Guide

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 being overweight or having obesity?

Medically speaking, doctors use a term you may already be familiar with: BMI, or body mass index. Familiarity with BMI, and your child’s BMI, can help you identify whether your child has obesity.

“Right now, the obesity epidemic is probably the worst it’s ever been,” says Daniel Ganjian, MD, a pediatrician in Santa Monica, California with a special interest in fighting childhood obesity. He recommends that all parents focus on prevention by encouraging healthy eating habits and regular physical activity.

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
• Obesity: equal to or greater than 95th percentile

A chart from the CDC allows medical professionals to determine a child’s BMI percentile (calculated as weight in kilograms divided by height in meters squared) by tracking their BMI and age together.

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 NewYork-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.

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.

Dr. Ganjian doesn’t advise waiting for BMI to get into the trouble zone before you make healthy lifestyle changes.

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 obesity range, your doctor may recommend additional approaches, such as measuring skin-fold thickness and evaluating family history, diet, and physical activity.

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.

Genetics

Socioeconomic Conditions

Unhealthy Food Choices

Lack of Exercise

Working with your child’s pediatrician to identify healthy-eating and exercise strategies can help reduce their risk for childhood obesity.

“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
• Sleep apnea
• Asthma

Long-term potential health consequences of a high BMI percentile in children include:

• High blood pressure and high cholesterol
• Metabolic dysfunction-associated steatotic liver disease (MASLD), or when fatty deposits build up in the liver and cause liver damage
• Cancer
• Arthritis.

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, Texas. The only one we can work on is weight, he says.

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.

Don’t Focus on the Weight

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. “We want them to either have a flatter BMI growth curve or keep growing up but gain weight at a slower pace,” says Dr. Lydecker. “That's a big difference in how parents think about it because it's so different from what we do for adults.”

Outside of the weight focus, parents should spend time with their children, 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,” says Lauren Salvatore, PsyD, assistant professor at the Donald and Barbara Zucker School of Medicine at Hofstra–Northwell in New York. Consider also offering nonfood rewards, like a trip or a new toy, for achieving the goals you set together.

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.”

Keep Healthier Foods on Hand

Kids generally eat what’s in the house, so stocking the pantry with healthy options can help them stay on track.

• Fresh fruits and vegetables
• Lean meats, chicken, fish, lentils, and beans
• Low fat or nonfat dairy

• Packaged and processed snacks, including chips, cookies, crackers, and frozen meals
• Soft drinks and sugary juices

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 Dr. Salvatore. “If the parent labels certain foods as bad, it may have larger long-term implications.”

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.”

Watch for Disordered Eating

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.

• Your child’s BMI can indicate whether your child has obesity.
• Many factors, such as genetics, socioeconomic status, and access to healthy food, can influence childhood obesity.
• Don’t wait until your child reaches the higher percentiles to start living a healthier lifestyle.
• Speak to a doctor or a pediatrician about how to best manage your child’s weight. A therapist may also be helpful to counsel your child through their weight loss journey.