Body mass index (BMI) estimates how healthy your weight is based on your height. There’s no “perfect weight” that fits everyone, but BMI can help most adults understand their weight-related health risks. BMI is calculated for both men and women by dividing weight in kilograms by height in meters squared.
About BMI
What Does My BMI Number Mean?
Body mass index (BMI) is a measure of your weight relative to your height.
For all men and women 20 years old and older, the BMI measurement is classified into one of four main weight categories:
- Below 18.5: Underweight
- 18.5 – 24.9: Healthy Weight
- 25.0 – 29.9: Overweight
- 30.0 and above: Obesity
People of Asian descent may have greater health risks at a lower BMI. People in this group may be placed in the overweight range if their BMI is between 23 and 25 and may have obesity if their BMI is 25 or greater.
BMI is calculated differently for kids. For children and teens under age 20, BMI is a percentile ranking that compares children of the same age and sex. This is because a child’s body fat makeup differs between boys and girls and changes often as they grow. There are four percentile rankings:
- Less than 5th percentile: Underweight
- 5th percentile to less than 85th percentile: Healthy weight
- 85th percentile to less than 95th percentile: Overweight
- Equal to or greater than the 95th percentile: Obesity
What Does My BMI Measurement Not Tell Me?
BMI is a screening tool that can let you know if you may be at risk for weight-related health problems. But because it doesn’t directly measure fat, there are some important things it can’t take into account:
Where your body fat is located: Maybe the most important thing that a BMI measurement can’t tell is where you’re storing fat in your body. Subcutaneous fat is just under your skin – it’s the fat you can see. But visceral (or abdominal) fat settles around your organs and has the greatest impact on your health. A high amount of this type of fat raises your risk for diabetes, heart disease, certain cancers, and other serious health problems.
Age: Body fat as a percentage of total body weight begins to go up around age 30.
Sex: At the same BMI, women (or people assigned female at birth) have about 10% more body fat than men (or people assigned male at birth).
Race/ethnic group: Different races or ethnic groups can have differences in body makeup at the same BMI. This includes such things as bone density, percentage of body fat, and overall body size.
Muscle mass: BMI is a measure of relative weight compared to height. It doesn’t measure how much of your weight is made up of muscle. A person with more muscle tissue as a percentage of body weight can have the same BMI as someone with more body fat.
Pregnancy: You shouldn’t use a BMI measurement to see if you’re at a healthy weight while you’re pregnant. Talk to your doctor about the weight range that is right for you at this time.
How to Use Your BMI Range
A BMI range tells you if you’re in a certain weight category. Compared to other tests your doctor can perform, it’s an effective measure of whether that weight category may increase your risk of certain serious health problems.
But taken alone, it doesn’t mean that you’re “fat” or “skinny.” It can’t tell you if you’re healthy or not or diagnose you with any condition. Talk with your doctor about your weight and your BMI. They can help you understand it as part of the bigger picture of your health as an individual and make decisions that are right for you.
BMI Calculator
A number doctors use to help judge your risk of illness. Body fat isn’t measured.
Waist-to-Height Ratio
Helps describe your body shape and could warn of health problems.
Metabolism
The process in your body that turns calories into energy.
Daily Calorie Target
The net number of calories your body needs to meet your weight goal.
Target Heart Rate
How fast your heart should beat when you’re getting a good workout.
