Glossary
Body Fat Percentage
Updated February 28, 2026
Body Fat Percentage estimates body composition as a percentage, not a medical diagnosis and not an unbroken truth. Useful trend signal comes from method discipline.
Use fat-free mass as a companion value when you want to separate composition change from body-weight noise.
Method confidence bands
Method choice sets the margin of error, so interpretation should always include confidence limits.
| Method | Typical confidence band | Best use window | Primary artifact |
|---|---|---|---|
| DEXA | ±1 to 3 percentage points | periodic baseline and body composition reviews | hydration shifts and device software updates |
| Bioimpedance | ±2 to 5 percentage points | frequent trend checks | hydration and electrolyte swings |
| Skinfolds | ±3 to 5 percentage points with expert operator | low-budget recurring tracking | site consistency and tester technique |
| Scale model estimates | ±3 to 8 percentage points | daily direction checks only | timing, hydration, and activity residue |
What creates false movement
Weekly pattern and timing distortions can look like fat changes.
| Distortion source | Typical direction | How to control |
|---|---|---|
| Morning hydration and salt | transient rise in one side of trend | standardize morning weigh-ins and fluids |
| Exercise within 24 hours | transient drop from glycogen and water shifts | avoid hard sessions before comparison scans |
| Meal timing and sodium spikes | temporary increase in water compartments | compare same precondition windows |
| Heat exposure and sleep debt | unstable baseline impedance | delay interpretation until recovery stabilizes |
Noise-floor rules and interpretation
Do not act on minor movement. Treat a swing as noise unless it exceeds method-specific floor and confirms across windows.
| Method | Noise floor to trust | Decision rule |
|---|---|---|
| DEXA | ≥2 points over two measurements | treat as real shift if repeated |
| Bioimpedance | ≥3 points over three daily points | only adjust if hydration and sleep are stable |
| Skinfolds | ≥2 points by same assessor | accept if technique and site are consistent |
| Scale estimate | ≥3 to 4 points over 3 to 4 weeks | use trend only with other methods |
Reporting rhythm
For coaching use, keep one method and one weekly window. If different methods disagree, prioritize method trend over absolute number, then reconcile against weight trend and training stress.
Reference bands
| Category | Men | Women |
|---|---|---|
| Essential | ~2%–5% | ~10%–13% |
| Athletes | 6%–13% | 14%–20% |
| Fitness | 14%–17% | 21%–24% |
| Average | 18%–24% | 25%–31% |
| Higher | ≥25% | ≥32% |
Use the same method each time to compare trends.