Body fat assessment
Body fat percentage is the share of total body weight made up of fat tissue. Unlike BMI, which uses only height and weight, body-fat percentage more accurately describes body composition — how much fat you carry relative to muscle, bone and organs. The calculator computes it with two methods at once — by circumferences (U.S. Navy) and by BMI (Deurenberg) — and shows the norm for your sex and age.
What body fat percentage is
Body-fat percentage is not just a number but an important health indicator. It divides all body fat into two kinds. Essential (necessary) fat is the baseline level that supports vital, reproductive and immune functions. Storage fat is deposited in adipose tissue: this is subcutaneous fat (under the skin) and visceral fat — inside the abdominal cavity, around the organs.
Both excess and insufficient fat are harmful. Excess leads to obesity and related diseases, while too low a level disrupts the hormonal system. That's why it's important to know not just your weight but your fat share: there is normal-weight obesity (TOFI, "thin outside, fat inside") — when weight is normal but there is too much fat, and the risks are almost as high as with overt obesity.
Two methods and how to measure correctly
The calculator computes body-fat percentage in two independent ways and compares them:
- The U.S. Navy method. Uses body circumferences (neck, waist, and for women the hips as well) together with height in logarithmic formulas. It is more accurate, especially for people with well-developed musculature. Accuracy is about ±3–4%.
- The BMI method (Deurenberg formula). Estimates fat from BMI, age and sex. Less accurate, but it doesn't require measuring circumferences and is handy for a quick estimate and for tracking trends.
Body-fat percentage calculator
Enter sex, age, height and weight — plus neck and waist circumferences (and hips for women) to add the more accurate U.S. Navy method. The calculation runs on the server; your data is not stored.
Each category's color matches its segment on the scale; your category is highlighted. The boundaries depend on sex.
Body-fat categories by the Navy method
The normal body-fat percentage differs between men and women. The commonly accepted body-composition classification:
| Category | Men | Women |
|---|---|---|
| Essential (minimum) fat | 2–5% | 10–13% |
| Athletic build | 6–13% | 14–20% |
| Fitness build | 14–17% | 21–24% |
| Average build | 18–24% | 25–31% |
| Obesity | 25% + | 32% + |
Healthy body-fat percentage by age
With age, the fat share usually rises — because of metabolic changes and a decline in muscle mass and activity. For older adults, a slightly higher body-fat percentage is considered normal. Below are typical healthy ranges:
| Age | Women | Men |
|---|---|---|
| 16–29 years | 16–24% | 7–17% |
| 30–39 years | 17–25% | 12–21% |
| 40–49 years | 19–28% | 14–23% |
| 50–59 years | 22–31% | 16–24% |
| 60+ years | 22–33% | 17–26% |
Visceral fat: why it is the dangerous one
Not all fat is equally harmful. Visceral fat — deep abdominal fat around the organs — is metabolically more active than subcutaneous fat: it drives inflammation more strongly and directly loads the liver with free fatty acids. That's why a high fat share is dangerous even at a "normal" weight — this is the TOFI phenomenon ("thin outside, fat inside"). To gauge visceral risk specifically as a single number, the LAP index (waist + triglycerides) helps, and for the fat share in the liver — FLI.
Body composition and biological age
For the pace of aging, what matters is not so much weight as your fat share and preserved muscle mass. Excess fat sustains low-grade inflammation and insulin resistance, shifts the hormonal balance and accelerates cellular aging, while low muscle mass makes the picture worse. The good news is that this is a reversible factor: cutting fat by even 5–10% of body weight noticeably improves metabolic markers. For more on how weight and metabolism relate to aging, see the BMI and metabolic age calculators.
science Measure more precisely · blood biomarkers Find out your biological age from lab tests — PhenoAge Body composition is just one aging factor. The PhenoAge calculator estimates biological age from 9 blood markers and shows exactly what is speeding up your pace of aging. Open calculatorHow to lose fat while preserving muscle
The key to losing fat for longevity is to lose fat specifically, not muscle: lean mass determines metabolism, strength and resilience to age (its loss is sarcopenia). In brief, what protects muscle during weight loss:
- Strength training. Preserves and builds muscle, making fat loss sustainable.
- Enough protein (1.6–2.2 g per kg of body weight). Protects muscle during a calorie deficit.
- Zone 2 cardio. Boosts fat oxidation and raises VO₂max — a longevity marker.
- Sleep and stress. Sleep deprivation and high cortisol shift fat into the visceral area and accelerate aging.
Why excess fat is dangerous
The WHO ranks obesity among the leading preventable causes of death. Excess fat — especially visceral fat — raises the risk of heart and vascular disease, insulin resistance and type 2 diabetes, fatty liver disease, sleep apnea and some cancers, reducing quality and length of life. How these factors add up into a single diagnosis and how to assess overall cardiometabolic risk is covered in the metabolic syndrome calculator.
Limitations of estimation methods
- This is an estimate, not a measurement. The reference standards are DEXA, hydrodensitometry or bioimpedance. The formulas give an approximation.
- The Navy method is sensitive to technique. An error of a couple of centimeters in a circumference measurement noticeably changes the result.
- The BMI method doesn't account for muscle. In muscular people it overestimates fat, and in older adults with low muscle mass it can underestimate it.
- Extreme body types. For professional athletes, during pregnancy, in children and the very old, interpretation should be given by a specialist.
Frequently asked questions
Which method is more accurate — Navy or BMI?
The U.S. Navy method (by circumferences) is usually more accurate — about ±3–4%, especially if the circumferences are measured carefully. The BMI method is simpler but doesn't distinguish muscle from fat. We show both so you can see the spread of the estimate.
Why are hips needed for women but not for men?
That's how the original Navy formulas work: fat distribution differs in women, so hip circumference is added to the calculation. Without it the Navy method can't be computed for women — but you'll still get the BMI-based result.
My weight is normal but my body-fat percentage is high — is that dangerous?
Yes, this condition is called "normal-weight obesity" (TOFI). The risks to metabolism and blood vessels are almost the same as with overt obesity, because it is visceral fat that is dangerous, not the number on the scale.
How often should I measure body-fat percentage?
For tracking trends, once every 2–4 weeks is enough, under the same conditions (in the morning, on an empty stomach, with the same measurements). The trend matters more than any single number.
