BMI Prime is BMI divided by the upper limit of the norm (25 kg/m²). The result is a dimensionless number that immediately shows how far weight deviates from the upper limit of the healthy range.
Its convenience is in the clarity: a BMI Prime of 1.0 means you are exactly at the upper limit of the norm, 1.2 is 20% above, 0.9 is 10% below. This makes interpretation simpler than absolute BMI and complements estimates such as SBMI and ideal body weight.
Reference ranges
BMI Prime = BMI / 25. The categories correspond to the usual BMI categories:
| Underweight | < 0.74 |
| Optimal weight | 0.74 – 1.00 |
| Overweight | > 1.00 |
| Obesity (class I and above) | ≥ 1.20 |
What an elevated level means
A BMI Prime above 1.0 means exceeding the upper limit of the norm: a value of 1.36 means BMI is 36% above the threshold of 25. Values ≥1.2 correspond to obesity and require an assessment of the waist and body composition.
What a low level means
A BMI Prime below 0.74 is underweight. As with ordinary BMI, a weight deficit also carries risks: loss of muscle, reduced immunity and, in older people, frailty.
How the test is done
First calculate BMI = weight(kg) / height(m)². Then divide it by 25. For example, at a BMI of 30: 30/25 = 1.2 — obesity, weight 20% above the upper limit of the norm. No separate measurements are needed, only height and weight.
What affects the value
- Muscle mass: BMI Prime inherits the main drawback of BMI — it does not distinguish muscle from fat.
- Choice of denominator (25 or 23) changes the result for Asian populations.
- Edema and dehydration distort weight.
Calculate using this marker
Calculators where BMI Prime is used directly:
Frequently asked questions
What does a BMI Prime of 1.2 show?
Your BMI is 20% above the upper limit of the norm (25 kg/m²) — this corresponds to class I obesity. A value of 1.0 is exactly at the limit, below 0.74 is underweight.
Why do you need BMI Prime if there is BMI?
It is clearer: it immediately shows the deviation from the norm as a multiple and a percentage, which is convenient for tracking trends. But it just as much ignores body composition as ordinary BMI does.