Body Fat (BMI estimate) Calculator

Adult BMI-based estimate, not a measurement.

Enter your values in the interactive calculator to see an instant result. Calculations run in your browser, without an account.

Results are estimates for educational use; confirm important decisions with appropriate experts.

Formula • Worked example • Interpretation

Estimate body-fat percentage from BMI

This tool estimates adult body-fat percentage statistically from BMI, age and a sex coefficient. It does not directly measure body composition.

Calculation method

A commonly published adult estimate is body-fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 × sex coefficient − 5.4, with coefficient 1 for male and 0 for female.

Worked example

For BMI 25, age 30, and male coefficient 1: estimated body fat ≈ 20.7%.

What your result means

This is a population-based approximation. People with the same BMI may have very different muscle, fat distribution and health profiles.

Tips for better calculations

Do not make health decisions from this estimate alone; seek a qualified professional for body-composition assessment.

Assumptions and limitations

The formula has substantial estimation error, is not suitable for children, and is not equivalent to DEXA, skinfold or other measurements.

SiCalcs tools provide estimates and educational calculations; they do not replace professional financial, medical, tax, or legal advice.