Why the BMI Scale Shifts With Age

Standard adult BMI categories were validated on working-age populations. For adults over 65, a slightly higher BMI is protective: fat reserves cushion against illness-related weight loss, and higher body mass correlates with preserved bone density and muscle mass. This calculator applies the geriatric scale — optimal 23.0–27.9 — instead of the adult 18.5–24.9.

The Risks of Being Underweight

In seniors, a BMI below 23 is more dangerous than mild overweight. It is linked to sarcopenia, osteoporosis, immune dysfunction, and sharply higher mortality. Nutrition and resistance training matter more than chasing a low number.

BMI Limitations

BMI cannot distinguish fat from muscle and does not reflect fat distribution. Use it alongside waist circumference, grip strength, and mobility assessments for a complete picture of senior health.