What is a healthy BMI? For most adults, a healthy BMI is between 18.5 and 24.9. A BMI below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obese. BMI is a quick screening tool, not a diagnosis — it does not distinguish muscle from fat.
Body Mass Index (BMI) estimates whether your weight sits in a healthy range for your height. It is widely used because it needs only two numbers, but it is best read alongside other measures such as waist size.
BMI ranges
| BMI | Rating | What it means |
|---|---|---|
| Below 18.5 | Underweight | May signal under-nutrition; worth a check-up. |
| 18.5–24.9 | Healthy weight | Linked with the lowest health risk for most adults. |
| 25.0–29.9 | Overweight | Raised risk of heart disease and diabetes. |
| 30.0 and above | Obese | High risk; consider professional guidance. |
What affects your BMI
- Height and weight — the two inputs BMI is built from
- Muscle mass — athletes can read high without excess fat
- Age and sex — body composition shifts over time
- Ethnicity — some groups face risk at lower BMI thresholds
- Fat distribution — waist size adds important context
How to improve it
- Use BMI as a starting point, then check your waist circumference
- Aim for gradual, sustainable changes rather than crash diets
- Combine balanced eating with regular activity
- Speak to a doctor before major diet or exercise changes
Work out your own numbers — the BMI Calculator does it instantly, for free, with the formula and a worked example built in.
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