What Is BMI?
Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate whether you're underweight, at a healthy weight, overweight, or obese.
Formula: BMI = weight(kg) / height(m)²
The BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
What BMI Tells You
BMI is a useful screening tool — not a diagnosis. A high BMI may indicate higher body fat, which is associated with increased risk for:
- Type 2 diabetes
- High blood pressure
- Heart disease
- Certain cancers
What BMI Doesn't Tell You
This is where most people misunderstand the metric:
BMI doesn't measure body fat directly. Two people with the same BMI can have very different body compositions.
- A bodybuilder with significant muscle mass may have a "overweight" BMI despite being very healthy
- An older person with low muscle mass might have a "normal" BMI while having too much body fat
- Age and gender differences in fat distribution
- Ethnicity (research suggests different risk thresholds for different populations)
- Where fat is stored (visceral vs. subcutaneous fat)
How to Use BMI Sensibly
Think of BMI as one data point among many, not a verdict on your health.
Combine it with:
- Waist circumference measurements
- Blood pressure readings
- Cholesterol levels
- Energy levels and fitness capacity
The Bottom Line
BMI is a quick, free, and reasonably useful starting point. Calculate it, note where you fall, and then talk to a healthcare provider if you have concerns. Don't use it as your only health measure, and don't let a number define how you feel about your body.