Body mass index (BMI) is a measure of your weight relative to your height and functions as a rough estimate of body fat. When you enter your height and weight into a BMI calculator, you’ll get a number. That number is one way to gauge if you have a healthy or unhealthy weight.
Calculate Your BMI
Once you have your BMI number, use the chart below to determine if you need to gain weight, maintain your weight, or lose weight.
BMI Chart – Adults (Age 20+)
| BMI | Weight Status |
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal or Healthy Weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Have Obesity |
The BMI calculator for children and teenagers is different than the one for adults. While it uses height and weight, it also uses age and gender. That’s because male and female height and weight change during growth and development. For children, BMI is expressed as a percentile as compared to other children of the same age and gender.
BMI Chart – Children and Teens (Ages 2 to 19)
| Weight Status | Percentile Range |
| Underweight | <5th percentile |
| Normal or Healthy Weight | 5th to <85th percentile |
| Overweight | 85th to <95th percentile |
| Have Obesity | 95th percentile or greater |
If you’re concerned about your BMI or your child’s BMI, talk with your doctor.
Path to improved health
You may be diagnosed with obesity if your body mass index (BMI) is at or above 30kg/m2. You can lower your BMI by following standard weight-loss tips, such as:
- Eating healthy. Choose lean meats, fruits, vegetables, and whole grains. Reduce alcohol, sugar, processed foods, sodas, and juices. Consume fewer calories.
- Exercising regularly. This includes cardio and weight-bearing exercises to build muscle and lose fat. This is effective in controlling belly fat. Belly fat increases the risk of certain health conditions. Always talk to your doctor before beginning an exercise program.
- Being mindful of portion control. Don’t overeat during meals and snacks.
If your child’s BMI is high (above the 85th percentile), talk with your doctor about how you can help your them lose weight.
Things to consider
An elevated BMI or diagnosis of obesity can also lead to other serious health conditions (e.g., type 2 diabetes, sleep apnea, arthritis) that have symptoms of their own. Although a high BMI does increase your risk of other health complications, BMI by itself is not a very good indicator of overall health.
However, it is an important marker that should motivate you to have a discussion with your doctor.
These tools should be guides only. Don’t rely on them to make decisions about your health or your child’s health. Always talk with your doctor about your health condition(s) and/or circumstances before making any lifestyle changes.
Questions for your doctor
- When should I be concerned with my child’s weight?
- When should I start checking my BMI? How often should I check?
- What is my ideal weight?
- What is my child’s ideal weight?
- Does BMI account for muscle?
- How can I reduce my BMI?
- How can I help my child reduce his or her BMI?
- How long will it take to reduce BMI?
Resources
Centers for Disease Control and Prevention: Adult Obesity Facts
National Heart, Lung, and Blood Institute: Overweight and Obesity
Last Updated:
This article was contributed by familydoctor.org editorial staff.
Copyright © American Academy of Family Physicians
This information provides a general overview and may not apply to everyone. Talk to your family doctor to find out if this information applies to you and to get more information on this subject.
