You’ve probably heard of BMI, or body mass index. It’s a common way to assess whether your weight might be putting your health at risk. But what exactly does it mean–and how useful is it?
Let’s start with the basics.
BMI is a number calculated using your height and weight. It gives a rough estimate of body fat and is used to group people into categories like “underweight,” “healthy weight,” “overweight,” or “obese.”
Here’s the formula: BMI = weight (kg) / height (m²)
You can also use an online calculator to do the math for you.
The number you get will fall into one of the following categories:
- Underweight: Below 18.5
- Healthy Weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obese: 30.0 and above
Why does BMI matter?
Research shows that BMI can help identify people who may be at higher risk for cardiometabolic conditions, such as high blood pressure, type 2 diabetes, and heart disease. Studies link higher BMIs with increased risk of these conditions, even in younger adults. That’s why it’s often used as a starting point in medical care–to flag when someone might benefit from preventive support or personalized care. Your employer or health plan may also use it to determine if you are eligible for certain medications like GLP-1s.
But BMI isn’t the whole picture.
While BMI can give a quick snapshot, it doesn’t tell the whole story. It doesn’t measure where fat is stored in the body or distinguish between fat and muscle. And it doesn’t account for differences in age, sex, ethnicity, or body composition.
Studies have shown BMI may under- or overestimate body fat in different demographics, such as women or people from different racial/ethnic backgrounds. For example, people of South Asian descent, on average, have smaller bodies and fat is distributed differently than for those of European descent. In fact, they may develop type 2 diabetes at lower BMIs than people of European descent.
Age can also make BMI inaccurate. Young men generally have more muscle than body fat, while older adults have more fat and less muscle.
That means two people with the same BMI could have very different health profiles. That’s why many health experts also recommend looking at waist circumference, which better reflects belly fat, a key marker for cardiometabolic risk. Learn how to take your waist measurement here.
So, how should you use BMI?
Think of BMI as one helpful piece of your health puzzle, not the whole picture. It can be a useful starting point for spotting weight-related risks. But it’s not a standalone tool. No matter your BMI, making time for daily movement, eating balanced meals, managing stress, and getting good sleep are key steps to supporting your long-term health.
Do you have questions about what your BMI means for your care? Your 9amHealth Care Team is here to help.
