Last updated: 2026-06-21

BMI Prime

BMI Prime is body mass index expressed as a ratio to the upper limit of the normal range. It is defined as body mass index divided by 25, so a value of 1.0 corresponds exactly to the overweight threshold. The number reads directly as how far above or below the healthy ceiling a person sits, which many people find easier to interpret than the raw index.

Definition

$\mathrm{BMI\ Prime} = \dfrac{\mathrm{BMI}}{25}, \qquad \mathrm{BMI} = \dfrac{\text{weight}}{\text{height}^2}$

Because body mass index already combines weight and height, dividing by 25 simply rescales it. A BMI Prime of 0.80 means the body mass index is 80% of the overweight ceiling; 1.20 means it is 20% above it.

How to read the result

The bands mirror the standard body-mass-index categories:

• Below 0.74 — underweight (body mass index under 18.5).
• 0.74 to 1.0 — normal (18.5 to 25).
• 1.0 to 1.2 — overweight (25 to 30).
• 1.2 and above — obese (30 and above).

Worked example

At about 0.97 they are just under the overweight threshold — close to, but still within, the normal range.

Limitations

BMI Prime inherits every limitation of body mass index. It does not separate muscle from fat, ignores fat distribution, and can misclassify very muscular or older people. Read it alongside measures of fat distribution such as the Waist-to-Height Ratio Calculator and the underlying BMI Calculator.