What Your BMI Means
A BMI result is one number, but what it tells you depends on your age, your background and your build. This guide explains the categories, why different countries use different limits, when BMI is misleading and what to measure alongside it.
What BMI measures
BMI compares your weight with your height. It was designed to study populations, and it works well for spotting a higher chance of weight-related health problems across large groups. For one person, it is a starting point for a conversation, not a verdict.
Why countries use different limits
The WHO categories (healthy weight from 18.5 to 24.9) are used in most of the world. In 2004 a WHO expert consultation found that many Asian populations face higher health risks at a lower BMI, and suggested lower action points of 23 and 27.5. NICE in the UK now applies these lower limits to people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background.
Some countries set their own standards. Japan's obesity society classes a BMI of 25 or more as obesity, in four grades. China's health standard WS/T 428-2013 uses 24 for overweight and 28 for obesity.
When BMI can mislead
- Strength athletes and people with physical jobs often have a high BMI because muscle is heavy.
- Older adults can have a normal BMI with little muscle and more fat.
- BMI says nothing about where fat sits. Fat around the waist is linked with more health risk.
- BMI does not apply during pregnancy or to children, who are compared with growth charts.
Measures that add useful detail
The waist-to-height ratio is simple and needs only a tape measure. A ratio under 0.5 is considered healthy for adults. Blood pressure, blood sugar and cholesterol, measured by a health professional, show how your weight actually affects your health.
| Measure | How to get it | What it adds |
|---|---|---|
| Waist-to-height ratio | Waist รท height | Belly fat, linked with heart and metabolic risk |
| Waist circumference | Tape measure | A quick check of central fat |
| Body fat percentage | Scan or special scales | Separates fat from muscle |
| Blood tests and blood pressure | Doctor or pharmacy | The direct health effects |
What to do with your result
- If your BMI is in the healthy range and your waist is under half your height, keep up your current habits.
- If your BMI is above or below the healthy range, use it as a reason to check other measures, not as a final judgment.
- Talk to a doctor before starting a diet or exercise plan, especially if you have a health condition, are pregnant or are over 65.
- Change slowly. Small, lasting changes to food, activity and sleep matter more than reaching a number quickly.