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Body fat calculator

Reviewed 4 November 2026 · How these numbers are calculated

Measure your neck and waist (women: and hips) with a tape and this body fat calculator works out your body fat percentage with up to four methods: the US Navy tape method, relative fat mass, skinfold calipers if you have them, and your BMI. It shows each result, an average with a realistic range, and where you sit in the healthy range for your age. Example: a 40-year-old man of 180 cm and 85 kg (187 lb) with a 39 cm neck and 88 cm waist comes out at 20% (Navy 18%, relative fat mass 23%), in the healthy range for his age.

What makes this body fat calculator different

Most body fat calculators use one formula, print one precise-looking number and compare it with a chart that ignores your age. Every method has an error of 3–5 percentage points, and methods disagree, so this one:

How to measure for the most accurate result

The tape is cheap and repeatable if you measure the same spots the same way:

A 1 cm slip at the waist moves the Navy result by about 0.8 points, so technique matters more than the formula. All methods, with their accuracy, are compared in how to measure body fat.

Body fat percentage chart by age

Women: body fat % by age
AgeLowHealthyOverObese
20–39<2121–3233–3839+
40–59<2323–3334–3940+
60–79<2424–3536–4142+
Gallagher et al. 2000, Table 4: body fat matching a BMI of 18.5, 25 and 30 in African American and white adults (4-compartment method).
Men: body fat % by age
AgeLowHealthyOverObese
20–39<88–1920–2425+
40–59<1111–2122–2728+
60–79<1313–2425–2930+

Healthy body fat rises with age for both sexes. Women carry about 12 points more than men at the same BMI: essential fat for hormones and pregnancy. Asian adults have more body fat at the same BMI, so their ranges start 1–5 points higher; the calculator has a switch for them. More detail, the ACE chart and answers like "is 25% body fat chubby?" are in what is a healthy body fat percentage?

Which method is most accurate?

The methods in this calculator
MethodTypical errorWatch out for
US Navy tapeTape: neck, waist (+ hips)±3.5–3.6 pointsNeck and waist placement; very muscular necks read low
Relative fat massTape: waist, heightValidated against DXA scansOnly one measurement, so belly fat drives it
Skinfold calipersCalipers, 3 sites±3.4–3.9 pointsNeeds practice; poor for high body fat
From BMIWeight, height, age±4–5 pointsCan't see muscle: athletes read too high
Typical error = standard error of estimate in the source studies against underwater weighing, DXA or a 4-compartment model. About two people in three fall within it.

For tracking, the best method is the one you can repeat the same way every 2–4 weeks. A DXA scan is more precise, but different machines read differently, so keep to one. Home scales that measure body fat move with how much water you've drunk, so they're better for trends than single readings. Then, to bring the number down: how to lower your body fat percentage.

Why body fat calculators give different results

If two calculators give you numbers 5 points apart, neither is broken. They were built against different reference methods (underwater weighing, DXA or 4-compartment models) in different groups of people, and each uses different body parts. A man with a big belly and slim legs gets a higher result from waist-based methods; a strong lifter with a thick neck gets a lower Navy result; anyone muscular gets a BMI-based number that's too high. That's why this calculator shows each method and averages the measured ones.

Body fat calculator for women

For women the Navy method adds the hips, because women store more fat there. A woman of 40, 165 cm, 70 kg (154 lb), neck 33 cm, waist 78 cm and hips 102 cm comes out at 32% (Navy) and 34% (relative fat mass): about 33%, inside the healthy 23–33% for her age. Measure at the same point in your cycle each month: water retention changes the waist a little. Essential fat for women is about 10–13%; going much below 20% often affects periods.

The US Navy body fat formula

The US Navy (and Department of Defense) method uses the logarithm of tape measurements in inches:

It was built against underwater weighing and is within about 3.5 points for most people. The military uses it for fitness standards, with its own rules for where and how to measure. The relative fat mass formula is simpler: 64 − 20 × height ÷ waist, plus 12 for women.

Fat mass, lean mass and calories

Your body fat percentage splits your weight into fat and lean mass (muscle, bone, organs and water). The man in the example carries 17.3 kg of fat and 67.7 kg of lean mass. Lean mass drives your resting burn: the Katch-McArdle formula gives him 1,830 calories a day at rest. Use your result in the calculator and it switches to that formula; see the TDEE formula and BMR vs TDEE for how it adds up.

How much fat do you need to lose?

Weight at a lower body fat, keeping your muscle
PersonWeight thenFat to loseWeeks
Man, 90 kg (198 lb)25% → 20%84 kg 185 lb5.6 kg12 lb13
Man, 90 kg (198 lb)25% → 15%79 kg 174 lb10.6 kg23 lb25
Woman, 75 kg (165 lb)35% → 30%70 kg 154 lb5.4 kg12 lb15
Woman, 75 kg (165 lb)35% → 25%65 kg 143 lb10.0 kg22 lb29
Lean mass kept the same. In practice some lean mass goes too, less with enough protein and strength training. Weeks at 0.5% of body weight a week.

Enter a goal body fat in the calculator for your own numbers, and track the weight side with the weight loss percentage calculator. To lose the fat, the calorie deficit calculator sets the calories; to keep the muscle, eat enough protein (how much protein to lose weight) and lift. If you'd rather stay at the same weight and swap fat for muscle, see body recomposition.

How often should you measure?

Every 2–4 weeks is enough: body fat changes slowly and every method has noise of a point or two. Track your waist measurement alongside the percentage, because it's the most direct sign that fat is going, and judge the trend over months. For which body fat number to aim for, see what body fat you need to see abs and BMI vs body fat.

Sources