Source: https://guthlabs.ai/docs/instruments/body-fat-bmi-based-deurenberg/mechanism/

instrument mechanism / verified-clean

# Body Fat % (BMI-based, Deurenberg) mechanism

The inspectable method record for Body Fat % (BMI-based, Deurenberg), kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The arithmetic formula is correct for the adult Deurenberg equation, and the honest label is appropriate. Final catalog approval requires explicitly documenting sex encoding and the adult applicability constraint.

- The formula is the standard Deurenberg adult estimate only when sex is encoded as 1 for male and 0 for female: BF% = 1.20·BMI + 0.23·age − 10.8·sex − 5.4.

- The specification does not define the required sex encoding, creating an exact input ambiguity.

- The formula is intended for adults; the specification does not state or enforce an adult-age constraint. It should not be presented as validated for children or adolescents without a separate formula.

## Units and conventions

- BMI is expressed in kg/m².

- Age is expressed in completed years.

- Sex is numeric: male = 1 and female = 0.

- The output is a percentage-point value, such as 27.9%, not a fraction from 0 to 1.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "BMI": 22,
    "age": 30,
    "sex": 0,
    "sex_encoding": "female=0, male=1"
  },
  "expected_outputs": {
    "body_fat_percent": 27.9
  },
  "working": "BF% = 1.20×22 + 0.23×30 − 10.8×0 − 5.4\n= 26.4 + 6.9 − 0 − 5.4\n= 33.3 − 5.4\n= 27.9%"
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The plain arithmetic engine can return Infinity for extreme finite JavaScript inputs, and it produces a negative body-fat estimate at the zero boundary instead of rejecting nonphysical inputs.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/body-fat-bmi-based-deurenberg/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/body-fat-bmi-based-deurenberg/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/body-fat-bmi-based-deurenberg/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche2/tranche2-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`