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Body fat percentage explained — healthy ranges by age and sex, and how it's measured

Body fat percentage is the proportion of your total body weight made up of fat — everything else (muscle, bone, organs, water) is lean mass. It's considered a more useful health measure than BMI because it distinguishes between fat and muscle. Two people at the same BMI can have very different body compositions: one lean and muscular, the other carrying excess fat with low muscle. Body fat percentage separates these cases.

Why body fat percentage matters

Fat is not simply dead weight. Essential fat — the fat stored in organs, bone marrow, and the nervous system — is required for normal bodily function. Men need at least 2–5% essential fat; women need 10–13% (higher, because of sex-specific fat in breast tissue and reproductive organs).

Beyond essential fat, storage fat acts as an energy reserve and insulates organs. Problems arise when storage fat accumulates in excess — particularly visceral fat (deep abdominal fat surrounding organs), which is associated with insulin resistance, cardiovascular disease and metabolic syndrome even when body weight appears normal.

Healthy ranges by sex and age

Category	Men	Women
Essential fat	2–5%	10–13%
Athletic	6–13%	14–20%
Fitness	14–17%	21–24%
Acceptable	18–24%	25–31%
Obese	25%+	32%+

These ranges (based on American Council on Exercise guidelines) apply to adults aged roughly 20–39. Body fat naturally increases with age as muscle mass declines. A 60-year-old at 27% body fat is not in the same health position as a 25-year-old at 27%. Adjusted ranges for older adults are 2–5 percentage points higher per category.

How body fat is measured

No consumer method gives a perfectly accurate measurement — each has trade-offs between cost, convenience and precision.

• DEXA scan (dual-energy X-ray absorptiometry) — the gold standard. A medical scan that distinguishes fat, muscle and bone density precisely. Accurate to within 1–2%. Available at hospitals and some gyms; costs £50–£200.
• Hydrostatic (underwater) weighing — you're weighed submerged in water, then compared to your dry weight. Very accurate, but requires specialist equipment and full submersion.
• Skinfold calipers — a trained professional pinches fat at specific body sites (usually 3–7 points) with calipers and enters the measurements into a formula. Cheap and reasonably accurate (±3–4%) in skilled hands.
• Bioelectrical impedance analysis (BIA) — consumer smart scales and handheld devices send a weak electrical current through the body. Fat resists the current; lean tissue conducts it. Convenient but affected heavily by hydration, food intake and time of day. Good for tracking trends, not absolute values.
• Navy tape measure method — uses waist, neck and (for women) hip circumferences in a formula. Free, requires only a tape measure, and accurate enough for most people (±3–4%).

Body fat vs BMI — which should you track?

Both have value. BMI is faster (just height and weight) and useful for population-level research. Body fat percentage is more informative for individuals. The classic failure of BMI: a 90kg man who is 6'1" and mostly muscle has a BMI of 26.6 (overweight) but a body fat of 12% (athletic). BMI calls him overweight; body fat percentage accurately reflects his health.

If you're tracking your health seriously, body fat percentage is the better number. If you just want a quick check, BMI is fine as a starting point — especially if you're not an athlete or bodybuilder.

How to reduce body fat without losing muscle

• Maintain a moderate calorie deficit (300–500 calories below maintenance) rather than a crash diet. Large deficits cause more muscle loss.
• Keep protein high — 1.6–2.2g per kg of bodyweight. Protein is muscle-sparing during a deficit.
• Continue resistance training — lifting weights signals the body to retain muscle even when losing fat.
• Prioritise sleep — growth hormone (released during sleep) is essential for muscle preservation and fat metabolism.