Body Fat Calculator: How Long to Your Goal

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What your result means

With the starting values (male, 35, 5 ft 11 in, 187 lb, neck 15 in, abdomen 36.5 in) the US Navy formula estimates a body fat percentage of 21.7%. The typical range runs from 17.7% to 25.7%: the formulas have a reported standard error of 3 to 4 points, so the range covers about 2 in 3 people or more. Against a DXA scan, the true value in young recruits was usually higher. That is 40.6 lb of fat and 146.4 lb of lean mass. The healthy range for men aged 20 to 39 is 8% to under 20% per Gallagher et al. 2000.

For the goal “Athletic” (13% and 6.6 lb more lean mass), the calculator shows 8 to 18 months, not one date. The range carries the measurement error: whether your true value is nearer 17.7% or 25.7% changes the plan by many weeks. Against DXA the tape read 6 points low on average in Foulis et al.; computed from their means, the DXA value lay above the range for a little over two in three recruits. If your true value is above it too, it would likely take longer than the top of the time frame. A faster pace shortens only the fat loss: at 1% a week it is 6 to 14 months, because the building phase after it takes just as long.

The example, week by week

0.5% a week means 0.5% of whatever you weigh that week. If his 146.4 lb of lean mass stays, the man in the example weighs 168.3 lb at 13% body fat (his lean mass divided by 0.87). Starting from 187 lb: 183.3 lb after 4 weeks, 179.6 lb after 8 weeks, 176.1 lb after 12 weeks, 172.6 lb after 16 weeks, 169.2 lb after 20 weeks, and 167.5 lb in week 22. The fat loss takes 22 weeks. If his true value is 4 points lower, at 17.7%, it takes 12 weeks; 4 points higher, at 25.7%, 32 weeks.

After that the calculator plans 6.6 lb more lean mass. With our assumption for the first year of training, 0.5% to 1.0% of lean mass a month, that takes 19 to 42 weeks, depending on the build rate and the measurement error. Together that is 31 to 74 weeks, or 8 to 18 months in whole months. His goal weight is then about 175.9 lb, between 167.3 and 184.5 lb depending on the measurement error.

How the body fat formulas work

1. Body fat from a tape. We use the circumference equations as Foulis et al. 2023 print them, with measurements in inches (centimeters divided by 2.54): men 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76; women 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. They go back to the Navy equations of Hodgdon and Beckett from 1984. The US Army used them until 2023/24. After its Directive 2023‑11 it taped one site only, at the navel; since Directive 2026‑13 of July 2026, which rescinds 2023‑11, it uses no body fat formula at all, only the ratio of waist to height. So this is not today’s military test.
2. Waist-to-height. With a tape, the calculator also shows the ratio of your abdomen or waist to your height, rounded down to two places, so a value under 0.55 never shows as 0.55; for the man in the example 36.5 divided by 71, so 0.51. Since July 2026 the US Army requires less than 0.55, measured at the navel. Women measure the waist at its narrowest point for the formula; there the waist is at most as large as at the navel, so their ratio is at most as high as the Army’s. It is the US Army’s body-composition standard for soldiers; the calculator draws no health conclusion from it.
3. Body fat from three skinfolds. With a skinfold caliper, the calculator uses Jackson and Pollock (men) and Jackson, Pollock and Ward (women) to get body density from the sum of the folds and your age, then Siri’s 1961 equation (as printed in Navy report 84‑11) for body fat; more on this below.
4. The typical range. The tape equations have a reported standard error of 3 to 4 percentage points, the women’s skinfold equation 3.7 to 4.0 points, and the men’s 0.0077 g/ml in body density, roughly 3.4 points after Siri; for all of them we use 4 points up and down. Without measuring, the calculator uses the formula of Deurenberg et al. 1991 from BMI, age and sex, with its error of 4.1 points. Plus or minus one standard error covers about 2 in 3 people, measured against each formula’s own reference method; for one person the miss can be larger. Using the means Foulis et al. 2023 report, the DXA value fell inside the tape’s range for just under a third of the recruits and above it for a little over two in three.
5. The comparison. The healthy ranges come from Gallagher et al. 2000 (Table 4), by sex and age. We put 18- and 19-year-olds in the 20 to 39 group and 80-year-olds in the 60 to 79 group. Without measuring, the calculator places you by BMI itself, because the formula only converts BMI. Under a BMI of 18.5, the calculator always places you below the healthy range and shows no body fat percentage. Below the healthy range, under our floors and when our BMI rule blocks a weight-loss goal at a BMI under 20 (under 22 from age 70), it shows no percentage either.
6. The goals are ours. Each goal lies within the healthy range: the lower limit plus 0.25 (Lean & defined), 0.40 (Athletic), 0.55 (Strong) or 0.75 (Healthy & fit) times the width of the range, rounded to whole percent. Below 10% (men) and 18% (women) the calculator makes no plan; these floors are our decision.
7. The time frame. Fat loss at 0.5% to 1% of body weight a week; Helms et al. 2014 recommend this muscle-protecting pace for natural bodybuilders preparing for a contest, so for lean, trained people. Lean mass stays the same during it. Then the planned gain at our rates: 0.5% to 1.0% of lean mass a month if you are new to training, 0.25% to 0.5% after 1 to 3 years, 0.1% to 0.25% after that. Research supports only the direction, that untrained people build muscle faster (Iraki et al. 2019), not these numbers. Everything is computed for the estimate and for the estimate minus and plus its typical error. Beyond 5 years the calculator names no year count: time frames that long rest on too many assumptions.
8. The limits. By our rule, based on the GLIM criteria, the calculator sets no weight-loss goal below a BMI of 20, or 22 from age 70, and checks every estimate in the range. The rule limits weight loss only: if your estimate needs no fat loss and your goal plans a gain, the calculator plans the gain alone. If the rule blocks a weight-loss goal although your BMI is not under that line, the calculator still shows your estimate and names the goals that give you a plan. Under a BMI of 18.5 and from a BMI of 35 (thresholds in the WHO classification) it makes no plan.
9. Protein. 1.6 to 2.2 g per kilogram of goal weight a day (0.73 to 1.0 g per pound), per Morton et al. 2018, who pooled studies without a calorie deficit, at most for your weight at a BMI of 25, rounded to 5 g. If your plan needs fat loss, the calculator gives 2.3 to 3.1 g per kilogram of lean mass for that phase, per Helms et al. 2014 for lean, trained people dieting. This calculator does not count calories; the TDEE calculator does.

How accurate the tape is

For the original men’s equation, Navy report 84‑11 gives a standard error of 3.52 percentage points, developed on 602 male naval personnel aged 18 to 56 against underwater weighing. Foulis et al. 2023 report 3 to 4 points for both equations, citing Hodgdon and Friedl 1999. In their own study of young US Army recruits (ages 17 to 42), the tape read 6 points low against a DXA scan on average at the start of basic training, the same for women and men, and it did not pick up the changes women made during basic training at all. At the lean end, the tape tends to read high instead.

So the calculator never shows a single number but a range, and the time frame works with it. For tracking progress, your waist and your weight, measured the same way, count for more than the percentage. That is why the calculator offers a reminder to measure again after 4 weeks.

If you want a number comparable to DXA: Stevens et al. 2016 developed equations directly against DXA scans from the US NHANES survey; their systematic error by age and ethnic group stayed within 1 percentage point. The University of North Carolina offers them as the American Body Composition Calculator. It asks for your race or ethnicity, which this calculator deliberately does not.

What body fat percentage is normal?

The tables show the healthy range per Gallagher et al. 2000 (body fat at a BMI of 18.5 to under 25, calculated for African American and white adults) and below it our goal values, by age. Gallagher et al. call their lower ranges uncertain themselves; for people of Asian descent they found higher values.

Body fat for men

Body fat for women

Body fat from skinfolds: the 3‑site caliper method

With a skinfold caliper you measure three folds: men at the chest, abdomen and thigh, women at the triceps, just above the hip bone (suprailiac) and the thigh. The calculator uses the equations of Jackson and Pollock 1978 (men) and Jackson, Pollock and Ward 1980 (women) and converts body density to body fat with Siri 1961 (as printed in Navy report 84‑11): 100 × (4.95 / density − 4.50). For the starting values with chest 16, abdomen 28 and thigh 20 mm (sum 64 mm), that gives 19.6%. The equations were developed against underwater weighing, on men aged 18 to 61 and women aged 18 to 55; for women over 40 the authors advise care. The study of men used a Lange caliper; measuring yourself can be further off. The calculator offers no 4‑ or 7‑site equations, because they need more sites.

Without measuring: the rough estimate

Without a tape or a caliper, the calculator uses Deurenberg et al. 1991: body fat = 1.2 × BMI + 0.23 × age − 10.8 × sex (men 1, women 0) − 5.4. For the man in the example that gives 23.1% instead of 21.7% with a tape. The typical error is 4.1 points, and the formula tends to read slightly high at a high BMI. The study covered people aged 7 to 83 with BMIs from 13.9 to 40.9, children included; outside that BMI range, the calculator shows no number. If you have a tape, use it.

Two examples

A woman, 42, 5 ft 5 in, 159 lb, neck 13.5, waist 33, hips 41.5 in, new to strength training, goal “Athletic”. The formula estimates 35.9% (typical range 31.9% to 39.9%); her healthy range at 42 is 23% to under 34%. Her goal is 27% and 4.4 lb more lean mass: by the estimate 26 weeks of fat loss, 14 to 39 weeks depending on the measurement error, at 0.5% a week, then 18 to 41 weeks of building, 8 to 19 months in all.

A woman, 30, 5 ft 6 in, 150 lb, neck 13, waist 29.5, hips 40 in, training for 1 to 3 years, goal “Healthy & fit”. Estimated 29.8%, goal 30%. By the estimate she needs no fat loss; if her true value sits at the top of the range, it takes 12 weeks. Most of the time goes to the planned gain of 2.2 lb: 18 to 39 weeks, 5 to 12 months in all. At about 153.1 lb, her goal weight is even slightly above today’s.

Safety and limits

For healthy adults, as information about appearance and fitness. Not for detecting, preventing, monitoring, predicting or treating any disease. Not for pregnancy or breastfeeding. The calculator is for adults 18 and over. It sets no weight-loss goal below a BMI of 20 (22 from age 70) and makes no plan under a BMI of 18.5, below the healthy range, below 10% body fat for men and 18% for women, or from a BMI of 35. From a BMI of 35, a goal belongs in a doctor’s care.

Why there are floors: very little body fat has a cost. In bodybuilders who get very lean through long, strict diets, the calorie deficit and the loss of body fat itself may have a greater impact on testosterone than the share of calories from fat, and in women a lasting lack of energy is the proposed cause of periods stopping. In men, the physical effects of semi-starvation can resemble the signs of an eating disorder (Helms et al. 2014).

If food, weight or your body takes up a lot of your thoughts, talk to someone. In the US, the ANAD Eating Disorders Helpline offers free support and treatment referrals at 1-888-375-7767, Monday to Friday, 9 a.m. to 9 p.m. Central. NEDA offers a free, confidential screening tool on its Get Help page. In a crisis, call or text 988, the 988 Lifeline, free and confidential, 24/7/365. Outside the US, Find A Helpline lists free, confidential helplines in over 175 countries. In Germany, the TelefonSeelsorge is free and available around the clock: 0800 1110111, 0800 1110222 or 116 123.

Frequently asked questions

How accurate is the Navy body fat calculator?

Within a few points, and more often too low. For the original men’s equation, the Navy’s 1984 report gives a standard error of 3.52 percentage points. Foulis et al. 2023 give 3 to 4 points for both equations, citing Hodgdon and Friedl 1999. In their own study of young US Army recruits at the start of basic training, the tape read 6 points low against a DXA scan on average, and it did not pick up the changes women made during basic training. That is why this calculator always shows a typical range. The Army itself has not used a tape formula since July 2026.

What body fat percentage is healthy?

Per Gallagher et al. 2000, the healthy range for men aged 20 to 39 is 8% to under 20%, for women 21% to under 33%; the limits move up with age. The ranges were calculated for African American and white adults; for people of Asian descent the study found higher values. Gallagher et al. do not present their ranges as definitive.

How long does it take to lose 1% body fat?

There is no fixed time per point, because it depends on how much of you is fat. At a pace that protects muscle, you lose 0.5% to 1% of your body weight a week; Helms et al. 2014 recommend it for natural bodybuilders preparing for a contest. For the man in the example above, 187 lb at an estimated 21.7%, the 8.7 points to 13% take 22 weeks at 0.5% a week and 11 weeks at 1%. Counting the typical range of the measurement, that is 12 to 32 or 6 to 16 weeks.

Can you calculate body fat from height and weight alone?

Roughly, from BMI, age and sex (Deurenberg et al. 1991). That formula is typically off by 4.1 points and tends to read slightly high at a high BMI. The study covered people aged 7 to 83 with a BMI of 13.9 to 40.9, children included; outside that BMI range, this calculator shows no number. A tape measure or a skinfold caliper gives a better estimate.

Why does my smart scale show a different number?

A smart scale does not measure fat directly. It sends a current through your body, measures the resistance (bioelectrical impedance) and converts it to body fat with its own formula; that is how Jagim et al. 2023 describe the method. Even tape and DXA were 6 points apart on average in Foulis et al. 2023. Compare numbers only within the same method and under the same conditions.

Where do you measure your waist for the Navy method?

Men measure the abdomen at the level of the navel, women the waist at its narrowest point plus the hips at the widest point of the buttocks. Both also measure the neck, just below the larynx. Measure the abdomen at the end of a normal breath out, with the tape flat on the skin and not pulled tight. For its waist-to-height ratio, the US Army measures everyone at the navel.

Why does the calculator base protein on the goal weight?

That is our choice: with a lot of body fat, today’s weight would push the grams far up. The meta-analysis by Morton et al. 2018 found no further muscle gain above about 1.6 g per kg of body weight a day; it pooled studies of healthy adults doing resistance training and left out studies with a calorie deficit. The upper end of its confidence interval was 2.2 g. The calculator applies that range to your goal weight, at most to your weight at a BMI of 25, and shows it only together with a plan. If your plan needs fat loss, the calculator gives 2.3 to 3.1 g per kg of lean mass for that phase (Helms et al. 2014, for lean, trained people dieting). The two ranges have different bases: Helms counts lean mass only, Morton the whole goal weight. For goals with a higher body fat percentage, the fat-loss range can therefore end lower than the range for the gain after it.

Privacy

Your measurements stay in your browser. We see none of it. The calculator runs entirely on your device. It sends your input neither to us nor to anyone else, stores nothing and writes nothing into the address bar. No photo needed. The share image shows only your goal, the time frame, short lines on the kind of plan (such as “Building, no fat loss”), your pace if you are losing fat and the kind of estimate, no measurements and no body fat number; your browser prepares it while you use the calculator and shares or saves it only when you tap. The calendar file holds only the reminder, no values, and is made only when you tap. Neither leaves your device unless you share it yourself. More in our privacy policy.

Sources

All sources retrieved between October 21, 2026 and October 23, 2026 and archived with their verbatim passages in the project’s verification archive. Eight documents come from Internet Archive copies, because the publishers’ or agencies’ pages could not be fetched on the retrieval day. The links below go to the originals; for Navy report 84‑11 and Army Directive 2023‑11 they go to the archive copy, because the Navy report could not be reached and the Army no longer serves the rescinded directive. Our rule for weight-loss goals is in our internal decision record and has no public link.

• Foulis SA et al.: Body composition changes during 8 weeks of military training … (Front Physiol 2023)
• Hodgdon JA, Beckett MB: Prediction of percent body fat for U.S. Navy men … (Report 84‑11, 1984; archived copy)
• Gallagher D et al.: Healthy percentage body fat ranges … (Am J Clin Nutr 2000)
• Deurenberg P et al.: Body mass index as a measure of body fatness … (Br J Nutr 1991)
• Helms ER et al.: Evidence-based recommendations for natural bodybuilding contest preparation (2014)
• Iraki J et al.: Nutrition Recommendations for Bodybuilders in the Off-Season (Sports 2019)
• Morton RW et al.: protein supplementation and resistance training, meta-analysis (Br J Sports Med 2018)
• Morton RW et al. (Br J Sports Med 2018), full text
• Cederholm T et al.: GLIM criteria (J Cachexia Sarcopenia Muscle 2019)
• Wild Garden: our rule for weight-loss goals (decision of October 11, 2026, internal record)
• NIST Guide to the SI, Appendix B.8 (inch)
• NIST Guide to the SI, footnote 22 (pound)
• TelefonSeelsorge Germany: phone
• 988 Suicide & Crisis Lifeline
• National Eating Disorders Association: Get Help
• Jackson AS, Pollock ML: Generalized equations for predicting body density of men (Br J Nutr 1978)
• Jackson AS, Pollock ML, Ward A: Generalized equations for predicting body density of women (Med Sci Sports Exerc 1980)
• Jagim AR et al.: Validation of skinfold equations … in young athletes (Front Sports Act Living 2023)
• WHO: Obesity: preventing and managing the global epidemic (Technical Report Series 894, 2000), Table 2.1
• U.S. Army: Army rolls out new Army Body Composition Program (June 15, 2023)
• Secretary of the Army: Army Directive 2023‑11 (June 2023; archived copy)
• ANAD: Eating Disorders Helpline
• Find A Helpline
• Secretary of the Army: Army Directive 2026‑13 (July 2026)
• U.S. Army: Army modifies body composition program, adopts waist-to-height ratio (July 7, 2026)
• Stevens J et al.: Prediction of percent body fat measurements in Americans 8 years and older (Int J Obes 2016)
• University of North Carolina: American Body Composition Calculator

Published October 25, 2026

An estimate with typical error, from a tape measure using the US Navy formula, from skinfolds using Jackson and Pollock, or roughly from BMI. For healthy adults, not for treating obesity or eating disorders. For health questions, see a doctor. Not for pregnancy or breastfeeding. The content is general information and does not replace individual medical, legal, tax or financial advice.

More from the garden

All calculators live under Tools. Also in the garden: the TDEE Calculator estimates how many calories you burn. The Habit Formation Calculator shows how long new routines like training take to stick. And the Sleep Calculator helps with the part of recovery that happens at night.

Content and tools on Wild Garden are published by the Wild Garden Editorial Team. How we research, check and correct errors is set out in our editorial standards.