"What's the right weight for my child?" is one of the most common questions parents have. It seems like a simple one, but it's not always easy to answer. Growth and Puberty Not everyone grows and develops on the same schedule. During puberty, the body begins making hormones that spark physical changes like breast development in girls, testicular enlargement in boys, and spurts in height and weight gain in both boys and girls. These changes continue for several years. The average kid can expect to grow as much as 10 inches (25 centimeters) during puberty before reaching full adult height. Because some kids start developing as early as age 8 and some not until age 14, it can be normal for two kids who are the same gender and age to have very different weights. What Is Body Mass Index? Body mass index, or BMI for short, is a formula that doctors use to estimate how much body fat someone has. The BMI formula uses height and weight measurements to calculate a BMI number. Though the formula is the same for adults and children, figuring out what the BMI number means is a little more complicated for kids. For kids, BMI is plotted on a growth chart because what is normal changes with age. Different BMI charts are used for boys and girls because growth rate and the amount of body fat differs between boys and girls. Each BMI chart is divided into percentiles that compare measurements with children the same age and gender. The categories that describe a person's weight are: Underweight: BMI below the 5th percentile age, gender, and height. Healthy weight: BMI is equal to or greater than the 5th percentile and less than the 85th percentile for age, gender, and height. Overweight: BMI at or above the 85th percentile but less than the 95th percentile for age, gender, and height. Obese: BMI at or above the 95th percentile for age, gender, and height. Before you calculate your child's BMI, you'll need an accurate height and weight measurement. Bathroom scales and tape measures aren't always precise. So the best way to get accurate measurements is by having kids weighed and measured at a doctor's office or at school. What Does BMI Tell Us? You can calculate BMI on your own, but consider asking your doctor to help you figure out what it means. Doctors do more than just use BMI to assess a child's current weight. They also take into account stage of puberty and use BMI results from past years to track whether a child is overweight. Spotting trends early on can be helpful so you can make changes before weight gain becomes a problem. Overweight and obese kids and teens are developing weight-related health problems, such as type 2 diabetes, high cholesterol, and high blood pressure (hypertension). Overweight teens are also more likely to be overweight as adults. And adults who are overweight have a greater chance of serious health conditions, such as heart disease. Although BMI can be a good indicator of body fat, it doesn't always tell the full story. Someone with a large frame or a lot of muscle (like a bodybuilder or athlete) can have a high BMI but not too much fat. Likewise, a small person with a small frame may have a normal BMI but could still have too much body fat. These are other good reasons to talk about your child's BMI with your doctor. When Kids Are Overweight or Underweight If you think your child has gained too much weight or is too thin, talk to your child's doctor. The doctor has measured your child's height and weight over time and knows whether growth is going as it should. If concerned about your child's height, weight, or BMI, the doctor may ask questions about your child's health, physical activity, and eating habits, and your family's medical history . The doctor can put all this information together to tell if there's a weight or growth problem. If your child's weight isn't in the healthy range, the doctor will give you specific diet and exercise recommendations. It's important to follow a plan that's designed for your child by the doctor or a dietitian. For kids and teens, strict diets won't provide the calories and important nutrients their bodies need to grow. What if your child is too skinny? Most kids who weigh less than others their age are just fine. They may go through puberty on a different schedule than some of their peers, and their bodies may grow and change at a different rate. Most underweight teens catch up in weight as they finish puberty during their later teen years, and there's rarely a need to try to gain weight. If your child is underweight or losing weight; is tired or ill a lot; has lasting symptoms like a cough, fever, diarrhea, or other problems, talk with your doctor. Kids and teens who are underweight because of eating disorders, like anorexia or bulimia, need medical attention. The Role of Genes Heredity plays a role in a person's body shape and weight. But genes are not destiny — kids can reach and keep a healthy weight by eating right and being active. Genes aren't the only things that family members may share. It's also true that unhealthy eating habits can be passed down. The eating and exercise habits of people in the same household can add to someone's risk of becoming overweight. If parents eat a lot of high-calorie foods or snacks or don't get much exercise, their kids tend to do the same. The good news is you can change these habits for the better. Even small changes, like cutting back on sugary drinks and going for a walk after dinner, can add up to make a real difference. Back to Articles Related Articles Losing Weight: Brandon's Story (Video) Brandon, 17, has lost 70 pounds through better eating and exercise. In this video he talks about what inspired him and how he stayed on track. Read More Managing Your Weight Has your doctor told you to lose weight? Get ideas on food, fitness, and staying motivated. We've also got weight management tools and recipes designed just for teens. Read More Weight Loss Surgery Weight loss surgery works. But it's serious stuff, both physically and emotionally. Find out about two weight loss surgery options for teens. Read More Weight Loss Surgery When diet and exercise aren't enough to help shed stubborn pounds, weight loss surgery may be an option for teens who are very overweight. Read More When Being Overweight Is a Health Problem A couple of pounds of extra body fat are not a health risk for most people. But when people are severely overweight, it can cause health problems. Read More Who Can Get Weight Loss Surgery? Doctors may do weight loss surgery if someone who is very overweight has tried but failed to lose weight and faces serious medical problems. Find out what makes teens eligible for bariatric surgery. Read More Overweight and Obesity Preventing kids from becoming overweight means making choices in the way your family eats and exercises, and how you spend time together. Read More Weight and Diabetes A balanced diet and an active lifestyle are important for kids with diabetes because weight can influence diabetes, and diabetes can influence weight. Read More Weight and Diabetes Weight can influence diabetes, and diabetes can influence weight. Managing weight can really make a difference in a person's diabetes management plan. Read More Weight and Diabetes Being at a healthy weight is a good idea for everyone, but it's even more important for kids with diabetes. Read More Growth Charts Doctors use growth charts to figure out whether kids' height and weight measurements are "normal" and whether they're developing on track. Here are some facts about growth charts. Read More Go, Slow, and Whoa! A Kid's Guide to Eating Right Want to eat healthier? It's easy when you learn the difference between Go, Slow, and Whoa foods! Read More Dealing With Feelings When You're Overweight If a person is struggling with extra weight, it can add to the emotional ups and downs of being a teen. Get some tips on coping here. Read More Keeping Portions Under Control Waistlines have been expanding over the last few decades. Part of the problem is what we eat, but another is quantity. Are our plates simply piled too high? Read More What Being Overweight Means Being overweight has become a serious problem for many kids and adults. Find out what it means to be overweight in this article just for kids. Read More 5 Ways to Reach a Healthy Weight Most dieters regain the weight they lost by dieting when they go back to their old eating habits. Get our tips on the best ways to drop excess weight. Read More Encouraging a Healthy Body Image A healthy and positive body image means liking your body, appreciating it, and feeling grateful for its qualities and capabilities. Parents can help kids develop a healthy body image. Read More Should I Gain Weight? Some kids think they're too thin and want to gain weight. Find out more in this article for kids. Read More What's the Right Weight for My Height? One of the biggest questions guys and girls have is whether they're the right weight. Because the body is growing and changing so much during adolescence, it can be tough to answer this question. Read More Should I Gain Weight? People want to gain weight for all sorts of reasons like playing their favorite sports or keeping up with friends who are filling out. So what's the skinny on weight gain? Find out here. Read More Staying at a Healthy Weight Here are some practical, everyday tips on making exercise and healthy eating work for you instead of feeling like it's the other way around. Read More Why Exercise Is Wise Exercise can help keep a kid's body fit and healthy. Learn more about what exercise can do for you in this article for kids. Read More How Can I Lose Weight Safely? Lots of people are unhappy with their present weight, but aren't sure how to change it - or even if they need to. Get the facts on weight loss here. Read More Body Mass Index (BMI) One of the biggest questions guys and girls have as they grow and develop is whether they're the right weight. One place to start is by learning about body mass index, or BMI. Read More Body Mass Index (BMI) Doctors use body mass index (BMI) measurements to assess a child's physical growth in relation to other kids the same age. Here's how to calculate BMI and understand what the numbers mean. Read More Healthy Eating Good nutrition and a balanced diet help kids grow up healthy. Here's how to improve nutrition and encourage smart eating habits. Read More Eating Disorders Eating disorders are common among teens and kids, especially young women. Read about the warning signs, prevention strategies, and ways to help a child with an eating disorder. Read More Why Exercise Is Wise Getting the right amount of exercise can rev up your energy levels and even help you to feel better emotionally. Find out why. Read More Your Child's Growth From the moment parents greet their newborn, they watch the baby's progress eagerly. But how can they tell if their child is growing properly? Read More Learning About Calories You've probably heard about calories. Are they good or bad for you? Find out in this article for kids. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.