CUN-BAE Calculator & Formula
Estimates body fat from BMI, age and sex — no tape measure — using a curve fitted and validated on a Spanish cohort against a lab reference.
CUN-BAE (Clínica Universidad de Navarra – Body Adiposity Estimator) is a polynomial in BMI, age and sex. It's the one body-fat formula WIMSTA runs that we've verified against its primary source and that was validated against air-displacement plethysmography, so it ships here without an asterisk. It's still BMI-based — shown as one voice in a range.
Your BMI is 25. Both read only BMI, age and sex, but CUN-BAE is a polynomial fitted on a Spanish cohort, so it bends where the BMI-to-fat relationship really bends. Here Deurenberg reads -2.2 pp vs CUN-BAE; push weight up and that gap grows, because Deurenberg's straight line keeps climbing. Two honest estimates from independent samples — the range between them is the real signal.
Built on a Spanish cohort
CUN-BAE was derived on n = 6,510, Spain (white adults 18–80) and validated against air-displacement plethysmography — a genuine lab reference, not another formula. Of every body-fat method WIMSTA runs, it's the one built on a Spanish population, which is why it tends to fit Spanish users better than equations trained elsewhere. Reported accuracy: SE ≈ 4.7% · r 0.89.
A curve, not a straight line
Unlike Deurenberg's linear equation, CUN-BAE includes BMI² and age/sex interaction terms, so it bends where the real BMI-to-fat relationship bends — and doesn't run away at high BMI the way a straight line does. Both read the same three inputs; comparing them (and the gap) is the honest read.
Strong for
Adults, especially Spanish/European, wanting a no-equipment body-fat estimate (SE ≈ 4.7% · r 0.89).
Weaker for
Very muscular builds (BMI can't see muscle), non-white populations (validated mainly in white adults), under-18s and pregnancy.
One estimate is a guess. See the range.
CUN-BAE, Deurenberg, US Navy and RFM rarely agree on the same body. The calculator shows the honest range they land in — and where it sits against the healthy zones.
Open the body-fat calculatorGómez-Ambrosi et al. (2012). Diabetes Care 35(2):383–388. Derived on n = 6,510, Spain (white adults 18–80), validated against air-displacement plethysmography (SE ≈ 4.7% · r 0.89). Coefficients verified against the primary source and covered by our test suite.
FAQ
What does CUN-BAE stand for?
CUN-BAE is the Clínica Universidad de Navarra – Body Adiposity Estimator. It estimates body-fat percentage from BMI, age and sex using a polynomial equation, published by Gómez-Ambrosi and colleagues in 2012.
Is CUN-BAE accurate?
It was validated against air-displacement plethysmography (Bod Pod) on a large Spanish cohort, with a standard error around SE ≈ 4.7% · r 0.89. That makes it one of the better BMI-based body-fat estimates — but it is still BMI-based, so it can't tell muscle from fat.
CUN-BAE or Deurenberg?
Both read the same inputs (BMI, age, sex), but CUN-BAE is a curve (it includes BMI² and age/sex interaction terms), while Deurenberg is a straight line that tends to overestimate at high BMI. They were also fitted on different populations — Spanish vs Dutch — so seeing both, and the gap between them, is more honest than trusting either alone.
Who is CUN-BAE not for?
It was validated mainly in white adults, so it may be less accurate for other ethnicities, and it isn't for under-18s or during pregnancy. Like every BMI method, it shares a blind spot for very muscular builds.
How every formula is sourced: the method page.