BMI — Body Mass Index — is one of the most searched health terms online, and for good reason: it's the quickest way to get a snapshot of whether your weight is in a healthy range for your height. But it's also widely misunderstood and frequently misapplied.
This guide explains what BMI actually measures, what the number ranges mean, how to calculate it accurately, and — critically — what BMI doesn't tell you about your health.
BMI is a number calculated from your height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s as a population-level statistical tool — not as a diagnostic tool for individuals. Despite this, it became the standard screening tool used by healthcare professionals worldwide to identify potential weight-related health risks.
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, bone density loss, anaemia |
| 18.5 – 24.9 | Normal weight | Lowest risk of weight-related conditions |
| 25.0 – 29.9 | Overweight | Increased risk of type 2 diabetes, hypertension |
| 30.0 – 34.9 | Obese (Class I) | High risk — cardiovascular disease, sleep apnoea |
| 35.0 – 39.9 | Obese (Class II) | Very high risk |
| 40 and above | Morbidly Obese | Extreme risk — often requires clinical intervention |
Rather than a single "target" weight, it's more useful to know the weight range that keeps you in the Normal BMI zone (18.5 – 24.9). The formula for this is:
The standard BMI ranges are designed for adults (18–65). For children and teenagers, BMI is interpreted differently — using age- and gender-specific percentile charts rather than fixed ranges. For adults over 65, some research suggests a slightly higher BMI (25–27) may actually be associated with better outcomes, as modest body reserves can be protective in illness.
There are also modest gender differences: women tend to have slightly higher body fat at the same BMI as men due to differences in body composition, which is why some health providers use gender-adjusted interpretations.
Metric or imperial. BMI gauge, category, and ideal weight range — instantly in your browser.
Check My BMI →BMI is useful as a population screening tool, but it has significant limitations when applied to individuals:
Muscle is denser than fat. Athletes and bodybuilders often have "overweight" BMIs with very low body fat.
People with higher bone density register higher BMI without corresponding fat increase.
Abdominal (visceral) fat is far more dangerous than subcutaneous fat — BMI doesn't distinguish between the two.
South Asians and East Asians tend to have higher health risks at lower BMI values. WHO has separate cutoffs for Asian populations (23 = overweight).
A better picture of your health comes from combining BMI with waist circumference, waist-to-hip ratio, body fat percentage (via DEXA scan or bioimpedance), blood pressure, blood glucose, and lipid panels.