Updated September 2026 Body Mass Index, plus waist-to-height ratio — the better predictor of health risk
Why we show waist-to-height ratio first
Body Mass Index is weight in kilograms divided by height in metres squared. Look at that formula and its central limitation is visible in it: there is no term for body composition and no term for where the mass sits. BMI cannot tell a kilogram of muscle from a kilogram of fat, and it has no idea whether you carry weight around your abdomen or your hips.
Waist-to-height ratio = waist ÷ height (same units)
Waist-to-height ratio fixes both problems with one extra measurement. It captures central adiposity — the fat deposited around the organs, which is the deposit most strongly associated with cardiometabolic risk — and it classifies the muscular athlete and the low-muscle case correctly, which no weight-based index can.
The rule is easy to remember and hard to game: keep your waist under half your height. A 180 cm person wants a waist under 90 cm; a 165 cm person under 82.5 cm.
Reading both numbers
| BMI | Category | Waist-to-height | Interpretation |
|---|---|---|---|
| Under 18.5 | Underweight | Under 0.40 | Possibly underweight for height |
| 18.5–24.9 | Normal range | 0.40–0.49 | Healthy range |
| 25.0–29.9 | Overweight | 0.50–0.59 | Increased risk — worth addressing |
| 30.0 and above | Obese | 0.60 and above | High risk |
These cut-points are population-level statistical conveniences, not individual diagnoses. Several health bodies apply a lower overweight threshold of around BMI 23 for South Asian populations, because cardiometabolic risk rises at a lower BMI in those groups.
Where BMI gets it wrong
- Muscular people. A 180 cm athlete at 95 kg and 10 percent body fat has a BMI of 29.3 — one point from obese, while leaner than nearly everyone around them.
- The “normal weight obese”. The inverse and more dangerous error. Low muscle mass with high body fat can sit comfortably inside the normal range, and BMI issues a clean bill of health.
- Height extremes. Because height is squared while human bodies do not scale quite that way, BMI tends to overstate adiposity in tall people and understate it in short people.
- Age. Older adults lose muscle and gain fat at stable weight, so an unchanged BMI can hide a real change in composition.
None of that makes BMI useless. Across large populations it correlates well with body fat and tracks obesity trends reliably — it is a good measurement being asked the wrong question. The full argument is in BMI: what it is good for, and what to use instead.
A worked example
A person of 178 cm and 88 kg, with an 86 cm waist.
WHtR = 86 ÷ 178 = 0.48 — healthy range
Healthy BMI weight range = 18.5 × 3.168 to 24.9 × 3.168 = 58.6–78.9 kg
The two numbers disagree, and the disagreement is the information. This is what a reasonably muscular person looks like on paper: flagged by BMI, cleared by the measurement that reflects where the mass actually is.
What to do next
If both numbers sit above the healthy range, the useful next step is a calorie target rather than a weight target — start with our TDEE calculator and read how fast you should lose weight. If they disagree, estimate your body fat percentage to settle it. And whichever way it falls, track the waist monthly rather than the BMI — it responds faster and means more.
BMI calculator — FAQ
It depends entirely on your body composition. BMI is reliable across large populations and unreliable about individuals, because it cannot distinguish muscle from fat or see where fat sits. If you carry significant muscle, expect BMI to overstate your adiposity — check your waist-to-height ratio instead.
Between 0.40 and 0.49. The simple rule is to keep your waist under half your height. Above 0.50 indicates increased cardiometabolic risk, and 0.60 or above is considered high risk.
First thing in the morning, before eating or drinking. Place the tape at the navel, level all the way round, snug but not compressing the skin. Breathe out normally and do not suck in. Take the measurement three times and average them.
Because muscle is dense and BMI counts it as undifferentiated mass. A muscular 180 cm person at 95 kg registers 29.3 regardless of carrying 10 percent body fat. This is the single most common false positive BMI produces.
Body fat percentage tells you more, but every method of estimating it carries three to eight percentage points of error. The practical combination is waist-to-height ratio as your primary number, a body fat estimate for context, and BMI only as a rough population comparison.