Methodology
How we compare BMI to other health metrics
Our methodology for the BMI Comparison Calculator calculator: the formula, step-by-step calculation, authoritative sources, and limitations. Reviewed quarterly.
Formula
Comparison = (valueA − valueB) / valueB × 100
Step-by-step
- 1
Calculate metric A using its specific formula (e.g. BMI = weight/height²).
- 2
Calculate metric B using its specific formula (e.g. body fat % from US Navy method).
- 3
Normalize both to a comparable scale (e.g. percentiles, risk categories).
- 4
Compare the two values side-by-side, noting where they agree and disagree.
- 5
Identify the metric that better matches the use case (screening vs. precise body composition).
Authoritative sources
Every claim on this page is backed by an authoritative source.
Assumptions
What we take to be true when applying this formula.
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Both metrics are calculated from consistent measurement techniques.
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The user understands the purpose of each metric (screening vs. diagnostic).
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Body composition is roughly stable during the comparison period.
Limitations
What this method does NOT capture.
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BMI is a screening tool, not a diagnostic. It can misclassify muscular individuals.
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Body fat % via tape measure has ~3–4% error margin. DEXA is more accurate.
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Single-point comparisons miss trends. Trends over months/years are more meaningful.
Last reviewed: 2026-06-15 • Reviewed by: CalcxApp editorial team