Body Fat from BMI Calculator (Deurenberg & CUN-BAE)
Estimate body-fat percentage from BMI, age and sex with the Deurenberg equation (adults and children) and the CUN-BAE equation from the University of Navarra — no tape or calipers needed.
How it works
BMI = kg ÷ m² · Deurenberg adults: %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex: men 1, women 0) · children: %BF = 1.51 × BMI − 0.70 × age − 3.6 × sex + 1.4 · CUN-BAE: −44.988 + 0.503·age + 10.689·S + 3.172·BMI − 0.026·BMI² + 0.181·BMI·S − 0.02·BMI·age − 0.005·BMI²·S + 0.00021·BMI²·age (S: men 0, women 1)
Deurenberg, Weststrate and Seidell (1991) showed that body fat can be predicted from BMI once age and sex are taken into account, because women carry more fat than men at the same BMI and fat rises with age. CUN-BAE (Gómez-Ambrosi et al., Diabetes Care 2012), developed at the Clínica Universidad de Navarra against air-displacement plethysmography, adds curvature and interaction terms and is widely used in Spain and Latin America. Both have an error of roughly ±4–5% and are less reliable for very muscular people.
Worked example
A 35-year-old man weighing 80 kg at 178 cm has a BMI of 25.2. Deurenberg: 1.2 × 25.25 + 0.23 × 35 − 10.8 − 5.4 = 22.1% body fat (ACE Average); CUN-BAE gives 23.1%.
Sources: Deurenberg P et al. Body mass index as a measure of body fatness. Br J Nutr 1991 · Gómez-Ambrosi J et al. Clinical usefulness of a new equation for estimating body fat (CUN-BAE). Diabetes Care 2012
Frequently asked questions
Can you calculate body fat from BMI?
Approximately. Adding age and sex to BMI explains most of the variation in body fat across a population, but an individual can be off by 4–5 percentage points — more if very muscular or very lean.
What is CUN-BAE?
The Clínica Universidad de Navarra – Body Adiposity Estimator, published in 2012. It predicts body fat from BMI, age and sex and was validated in more than 6,000 Spanish adults.
Why does the result change with age?
At the same BMI, older adults usually have less muscle and more fat, so both equations add body fat as age increases.
Does it work for athletes?
Not well. Extra muscle raises BMI without adding fat, so these equations overestimate body fat in muscular people. Use skinfolds or a tape method instead.
Related calculators
This calculator gives an estimate for general fitness and education only. It is not a diagnosis — results from field tests and prediction equations can differ from laboratory measurements, so talk to a doctor or qualified exercise professional before acting on them.