What is Underweight for a 15-Year Old?

Teenagers are at an important stage in their life of growth and development. It is important that they maintain a healthy weight by eating a proper amount of food to nourish their growing body. If you are not giving your body the fuel it needs during this phase of growth, it can cause issues now and later on down the road!

A 15-year old female who is 5 foot 3 inches tall and weighs less than 92 pounds would be classified as underweight. A 15-year old male who is 5 foot 7 inches tall and weighs less than 105 pounds would be classified as underweight. Different heights and weights would be classified differently.

The Center for Disease Control and Prevention (CDC) has defined “underweight” as: below the 5th percentile on growth charts. Growth charts use body mass index (BMI), which is a simple calculation using weight and height. It is important to look at other factors such as eating and exercise habits, mental health, medications, living circumstances, etc. before making a judgment about a teen’s health!

Read on for more information about what is a healthy weight for a 15-year old, factors that impact weight, tips for parents, and tips for teenagers wanting to gain weight in a healthy way.

What is a Healthy Weight for a 15-Year Old?

There are lots of changes going on in a 15-year old’s body, so looking at a one-time weight measurement to determine if they are “healthy” is not the best way of going about things. Growth charts can be helpful because they can help you track weight over time. Although growth charts use BMI, we normally talk about things in terms of percentiles for children and teenagers. These are the classifications that the CDC uses to classify weight as underweight, healthy weight, overweight, or obese:

While this might sound really simple and straightforward, overall health is a bit more complicated. Remember that weight is really only one aspect of health- one factor to consider. It doesn’t always tell the full story of what is going on.

Check out your child’s growth on a growth chart calculator here or access the correct growth chart here. Use the BMI-for-age growth chart to get the right weight status category based on percentile.

A healthy weight for a 15-Year old is defined as having a Body Mass Index (BMI) between the 5th and 85th percentiles on the Center of Disease Control and Prevention’s (CDC) growth charts. A healthy weight classification based on the growth charts is equal to a 5 foot 3 inch (160 cm) tall 15-year old female weighing between 92 and 135 pounds (42 to 61 kg) or a 5 foot 7 inch (170 cm) tall 15-year old male weighing between 105 and 149 pounds (48 to 68 kg). However, looking at weight alone is not advised. There are many more factors at play in determining if you are healthy than just the number on the scale.

What is Underweight for a 15-Year Old?

A 15-year old female who is 5 foot 3 inches tall (160 cm) and weighs less than 92 pounds (42 kg) would be classified as underweight. A 15-year old male who is 5 foot 7 inches tall (170 cm) and weighs less than 105 pounds (48 kg) would be classified as underweight. Different heights and weights would be classified differently.

Is it Unhealthy to be Underweight?

Although being classified as underweight does not automatically make you unhealthy, it does often correlate with less than ideal conditions for your body to grow and develop. 

For example, having a certain amount of body fat is important for your hormones to stay regulated. Being underweight could mean your body is also not getting the nutrients that it needs to function properly.

Work with your doctor and a registered dietitian to make sure your weight is at a healthy spot and that your body has what it needs to grow and develop. 

What Factors Can Impact a 15-Year Old’s Weight?

There are a lot of factors that can impact a teenager’s weight. Here are just a few of those factors and how they can affect weight.


Sometimes this one is forgotten about, but it is the one that can sometimes affect weight more than anything else! Your genetics determine so much about how your body functions, including weight.

Eating and Exercise Habits

Eating too little or eating more than your body needs can lead to fluctuations in weight. Exercising burns through a lot of energy which can also affect weight if you are not eating enough to keep up with what you are burning. By 15 years old, teenagers are making more of their own choices and developing habits that might stay with them for a long time, so it is important to develop good eating and exercise habits now!

Mental Health

Stress levels can have a really significant impact on weight. Emotions can lead to changes in appetite, and sometimes mental health medications have side effects related to weight. High levels of stress hormones can even result in your body storing fat differently and can also impact weight. 


Lots of teenagers struggle to get enough sleep, whether it is because of a crazy sports schedule, spending time with friends, extracurricular activities, homework, or something else! However, your body really needs that time for your body to rest and recover and for your hormones to regulate themselves.

Social Atmosphere

15-year olds are often at school, out with friends, with sports teams and clubs, and more. This puts them in a position to experience peer pressure and pick up habits from those around them. This may even include feeling pressure to make their body look a certain way.

Parent Beliefs and Habits

Teenagers are starting to gain a little bit more freedom, but many times they are still not the ones fully in charge of the food at home. The amount and type of food that is available at home can be a factor impacting weight. Parents also set an example for their kids (whether they know it or not) regarding eating, exercise, and other habits.

When Should a 15-Year Old Gain Weight?

Making changes to your body can be challenging and doing it on your own is not recommended. Gaining weight might not even be what is healthiest for you. Develop a good relationship with your doctor so that you can talk openly about what is going on in your life, as well as about your health and weight concerns. 

Doctors should always direct teenagers to a registered dietitian if they need to gain weight. A dietitian is a nutrition expert that can help you gain weight in a healthy weight and they can give you tips on how to best take care of your body.

Focusing too much on weight can sometimes feel overwhelming for teenagers. Instead, focus on how you can fuel your body and give it what it needs. This is a focus you can have throughout your entire life, no matter what your weight is!

What is the Healthiest Way to Gain Weight for a 15-Year Old?

The healthiest way to gain weight is to increase calorie intake from nutrient-rich foods. While you might gain weight if you eat fast-food and ice cream for every meal, it is likely not going to leave you feeling too good.

Your strategy also depends on your current weight and what your overall goals are. Consistency day-to-day is important for everyone though!

Tips for Gaining Weight for a 15-Year Old

So if you are wanting to gain weight, where do you start? Here are some of my top tips for teenagers wanting to gain weight.

  1. Eat frequently throughout the day and don’t skip meals or go a long time without eating. For a lot of teenagers wanting to gain weight this might be eating every 2-4 hours during the day. Skipping meals and not including snacks during the day makes it much harder to reach your total energy needs.
  1. Keep food available wherever you go. There is nothing worse than getting stuck somewhere with no food! Store healthy snacks in your car, at your work, in your locker, in your backpack, and wherever else might be helpful!
  1. Eat when you start to feel hunger pangs, rather than when you are feeling completely empty and ravenous. This will be more helpful in providing your body with constant nourishment and it will help you better listen to your body and regulate your appetite.
  1. Ditch the distractions! Put away your phone, turn off the TV, or step away from your homework while you eat. It may not always be possible to step away from distractions, but making it a priority when you are able to will help you develop good habits and make it easier to listen to your body.
  1. Focus on calorie-dense foods that are also nutrient-dense. This includes a lot of fatty foods like fish, nuts, nut butters, seeds, oils, and avocados. This can also include dense carbohydrate foods like bagels, dried fruit, and smoothies.
  1. Don’t try to do it on your own. Work with a dietitian to make sure you are meeting your needs in a healthy way. Everyone needs a good support system!
  1. Get in a carbohydrate snack right before exercise and utilize sports drinks and other forms of simple carbs during physical activity. Remember to have a carbohydrate and protein snack or a full meal after your workout too, preferably within an hour of exercise.
  1. Utilize liquid calories that are nutrient-dense. 100% fruit juice, smoothies, protein drinks, milk, etc. are great ways to get more calories in between meals when it is easier to sip on something than it is to eat something.
  1. Hydration is important, but if you tend to get full really fast at meals, maybe save your liquids until after you are finished eating or between meals.
  1. Try to “power-pack” your foods, meaning squeeze in a lot of calories into a smaller volume. Having to eat a huge volume of food every day can feel really daunting, so power-packing makes it a little bit more doable! Switch to whole milk, full-fat yogurt, and add avocado, nut butter, nuts, seeds, butter, olive oil, and cheese to foods to boost calories. Smoothies are a great example of powerpacking because you can add things like flax seeds, milk, yogurt, peanut butter, protein powder, and more!

Tips for Parents Who Want to Help Their Teen Reach and Maintain a Healthy Weight

If you want your teenager to gain weight, simply forcing them to eat might not always work out great. Here are some tips for helping support your teen in their journey to a healthy weight.

  • Do your best to have a wide variety of foods available that your teenager likes to eat!
  • Don’t focus too much on weight. Focus more on encouraging good eating habits!
  • Get your teenager involved in the grocery shopping and cooking! Let them make some decisions and get excited about new foods and new recipes.
  • Refrain from making comments about your own weight or the weight of other people.
  • Don’t make your teenager feel singled out. Encourage your entire family to adopt healthy eating patterns.
  • Talk about food in a neutral way, rather than referring to foods as “good” and “bad.” Talk about the benefits of certain foods and what they do for your body and how you feel when you eat them! 
  • Look for signs of disordered eating and a poor relationship with food. Get your teenager the help they need from experts and don’t feel like you have to do it on your own.


Weight is not the most important factor in determining your overall health and there are so many other factors at play. Changes in weight often come from changing your habits, which is something you have total control over! As you focus on nourishing your body and developing good nutrition habits, you are going to be improving your health, working towards a healthy weight, and hopefully feeling your best!

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Academy of Nutrition and Dietetics. BMI for Children and Adolescents. Eatrightpro.org. Published August 26, 2015.

Katherine Harmer, RDN

I'm a Registered Dietitian Nutritionist with a love for coaching others to success in their health goals, especially teenage athletes. Tennis was my sport of choice in high school. Now I'm a little bit older, a little bit smarter, and a little bit worse at tennis.

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