BMI for Age 66 — Healthy Weight Range
For adults aged 66, the WHO-standard healthy BMI range of 18.5–24.9 applies. BMI is calculated the same way at any adult age: weight (lbs) ÷ height (in²) × 703.
BMI Categories — All Ages
Under 18.5Underweight
18.5 – 24.9Normal weight
25.0 – 29.9Overweight
30.0 – 34.9Obese Class I
35.0 – 39.9Obese Class II
40.0 +Obese Class III
At age 66, metabolic changes — including declining muscle mass (sarcopenia starts around age 30) and shifting fat distribution, accelerating after 60 can affect body composition without changing BMI. A person at age 66 with BMI 23 may have more body fat than a 25-year-old at the same BMI if they have less muscle mass.
The CDC-defined average BMI for US adults is 29.8. By age group: adults 20–39 average 27.8, adults 40–59 average 30.3, adults 60+ average 29.5 (NHANES 2017–2020).