Why BMI Has Limitations (And What to Use Instead)

BMI is one of the most widely used health metrics in the world — and one of the most criticized. While it works well at the population level, it can mislead individuals. Here's what BMI gets wrong, and how to fill in the gaps.

BMI Doesn't Distinguish Fat from Muscle

Muscle is denser than fat. A heavily muscled athlete can have a BMI above 25 or even 30 while carrying very little body fat and being in peak physical condition. The formula has no way to separate these tissue types.

BMI Ignores Fat Distribution

Where fat is stored matters enormously. Visceral fat — the kind that accumulates around internal organs in the abdomen — is far more dangerous than subcutaneous fat under the skin. Two people with the same BMI can have very different risk profiles depending on where they carry their weight.

BMI Is Less Accurate for Older Adults

As people age, they typically lose muscle and gain fat while weight stays the same. An older adult may have a normal BMI but a dangerously high body fat percentage — a phenomenon called 'skinny fat' or, clinically, 'normal-weight obesity.'

Better Metrics to Use Alongside BMI

• Waist circumference: over 40 in (102 cm) for men or 35 in (88 cm) for women signals abdominal obesity
• Waist-to-height ratio: keeping waist under half your height is a strong predictor of metabolic health
• Body fat percentage: measured via DEXA, BIA scale, or calipers
• Blood markers: fasting glucose, triglycerides, HDL cholesterol, and blood pressure