How body fat % is estimated
The Deurenberg formula (1991) estimates body fat percentage from BMI, age, and sex, without needing calipers or a scan.
- BMI — weight (kg) / height (m)²
- age — age in years
- s — sex constant (1 male, 0 female)
More detail
Accuracy of this estimate
Deurenberg's formula is a population-level statistical model, not a direct measurement. It correlates well with underwater weighing on average, but can be off by several percentage points for very muscular or very lean individuals. Skinfold calipers or a DEXA scan give a more precise reading.
Why the result differs by sex
At the same BMI, women naturally carry more essential body fat than men (for hormonal and reproductive reasons), so the formula subtracts less for women — that's the ×s term.
Practical tip. Track the trend over weeks rather than a single reading. Body fat % estimated this way moves with your BMI, so it's most useful for seeing direction — down, up, or flat — alongside the scale.
Frequently asked questions
How accurate is this body fat estimate?
It's a statistical estimate derived from BMI, age, and sex — not a direct measurement. It tracks underwater weighing reasonably well on average but can be off by several percentage points for very muscular or very lean people. Calipers or a DEXA scan are more precise.
What's a healthy body fat percentage?
Typical ranges run roughly 14–24% for men and 21–31% for women, varying with age and fitness level. Enter your details above to see which category your estimate falls into.
Why does body fat % differ between men and women at the same BMI?
Women naturally carry more essential body fat than men for hormonal and reproductive reasons, so the Deurenberg formula subtracts less for women — this shows up as the sex constant (s) term in the calculation above.