The All-in-One Body Composition, Calorie & Protein Calculator
Most calculators give you a number and leave you to figure out what to do with it. This one doesn't.
Enter your measurements and activity level and you will get your estimated body fat percentage using the US Navy method - one of the most validated tape-measure techniques available - alongside your fat mass, lean mass, and a daily calorie target adjusted for your specific goal. Your protein requirements are calculated from your body weight and goal simultaneously, so you leave with a complete nutritional picture rather than a single isolated figure.
What the calculator works out
Body fat percentage is estimated using the US Navy circumference method, which uses neck, waist, and for women hip measurements alongside height. If you already have a reading from smart scales or a BIA device, you can enter it alongside your measurements. The calculator will show both figures, note the difference, and use the midpoint for all downstream calculations - which is a more defensible working figure than either method alone.
Fat mass and lean mass are derived directly from your body fat percentage and total weight. These matter more than body fat percentage in isolation because they tell you what you are actually carrying and what changes when you alter your diet or training.
Calorie targets are calculated using two established formulas - Mifflin-St Jeor and Katch-McArdle - and expressed as a range rather than a single figure. This reflects the reality that no formula is perfectly accurate for any individual. The range gives you a more honest working window. Your physical activity level is applied via a continuous slider across six bands from bed-bound to extremely active, so the multiplier reflects where you actually sit rather than forcing you into a category that doesn't quite fit.
Your goal - fat loss, maintenance, or muscle gain - adjusts both your calorie target and your protein requirements together. For fat loss, the recommended deficit is set automatically based on your body fat percentage: leaner individuals are steered toward a mild deficit to protect muscle, those with more to lose are guided toward a larger deficit where the evidence supports it. You can override the recommendation and position the slider wherever you want.
Protein targets use multipliers grounded in the peer-reviewed literature, ranging from 1.2g per kilogram for maintenance through to 2.4g per kilogram for active fat loss phases. For those 65 and over selecting maintenance, the older adult range applies automatically given the well-established case for higher protein intake to counter age-related muscle loss.
Why the range matters more than the number
Every formula used here produces an estimate. BMR equations typically carry an error margin of around 10%. Activity multipliers add further uncertainty. Treating any single output as precise is a mistake most generic calculators quietly encourage by presenting a single clean figure. Expressing results as a range is not hedging - it is the accurate way to represent what the science actually says.
Use the midpoint of your range as a starting point. Track your weight trend and training performance over two to three weeks. Adjust by 100-150 kcal in either direction based on what you observe. That process will converge on your true maintenance faster and more reliably than any formula alone.
On the body fat methods
The US Navy method is a reasonable field estimate when measurements are taken correctly. Measure your neck at the narrowest point and your waist at the navel, relaxed after an exhale, not pulled in. BIA from consumer scales varies significantly with hydration status, time of day, and device quality. Neither method is a DEXA scan. Both are useful for tracking change over time, which is their primary value.
Frequently Asked Questions
The American Council on Exercise categorises male body fat as follows: essential fat sits between 2 and 5%, the athlete range is 6 to 13%, fitness falls between 14 and 17%, acceptable spans 18 to 24%, and above 25% is classified as obese. These are population-level reference points, not clinical thresholds.
The more useful question is what is healthy for you at your age. The Jackson and Pollock data shows that ideal body fat increases with age - 8.5% at 20, 15.3% at 40, 18.9% at 50, 20.9% at 55. A man in his late forties sitting at 18% is not in the same position as a 25-year-old at 18%. Context matters more than the number in isolation.
For most men over 35 focused on aesthetics, health markers, and longevity, a realistic and sustainable target sits somewhere in the fitness to low-acceptable range - roughly 14 to 20%. Below 10% is achievable but typically requires a level of dietary restriction that is difficult to sustain and may negatively affect testosterone, sleep, and recovery.
TDEE stands for Total Daily Energy Expenditure - the total number of calories your body burns in a day across all activity, not just exercise.
It is calculated in two steps. First, your Basal Metabolic Rate is estimated - the calories your body burns at rest to maintain basic physiological function. The two most widely used formulas are Mifflin-St Jeor, which uses total body weight, height, age, and sex, and Katch-McArdle, which uses lean mass only and therefore requires a body fat estimate. Second, your BMR is multiplied by a Physical Activity Level factor that accounts for how active you are across the full day, not just structured training.
The result is an estimate with an inherent margin of error of around 10% in either direction. This is why expressing TDEE as a range rather than a single figure is more honest and more useful. Treat your calculated range as a starting point, track your weight trend over two to three weeks, and adjust by 100 to 150 calories in either direction based on observed results. That feedback loop will converge on your true maintenance figure faster than any formula alone.
The evidence-based range for fat loss is 1.6 to 2.4 grams of protein per kilogram of body weight per day. The higher end of that range is supported when the goal is body recomposition - losing fat while preserving or building lean mass simultaneously.
Higher protein intake during a calorie deficit serves three functions. It preserves lean mass by giving your body sufficient amino acids to maintain muscle tissue when total calories are restricted. It has a higher thermic effect than carbohydrate or fat, meaning your body burns more calories digesting it. And it is more satiating gram for gram, which makes adherence to a deficit more manageable.
Practically, for a man weighing 85kg in a fat loss phase, the target range works out to 136g to 204g of protein per day. Hitting the lower end is sufficient for most people. The upper end becomes more relevant if training volume is high, the deficit is aggressive, or body fat is already relatively low.
BMR is the number of calories your body burns at complete rest - essentially the energy cost of staying alive with no movement whatsoever. It accounts for breathing, circulation, cell repair, temperature regulation, and organ function. For most people, BMR represents roughly 60 to 70% of total daily calorie expenditure.
TDEE is your BMR multiplied by an activity factor that accounts for everything else - walking, exercise, the physical demands of your job, and the general movement of daily life. It is the number that actually matters for nutrition planning because it reflects what you genuinely burn across a full day.
The gap between the two can be substantial. A sedentary person might have a TDEE only 20% above their BMR. Someone doing hard daily training could have a TDEE 80 to 90% above their BMR. Eating to your BMR when your TDEE is significantly higher would put you in a deeper deficit than intended, while ignoring the distinction entirely leads most people to underestimate how much they need to eat to support training and recovery.
Studies comparing the US Navy method to DEXA scanning - the gold standard for body composition measurement - typically find a mean error of around 2 to 4 percentage points, with individual variation sometimes larger than that. It tends to perform better at moderate body fat levels and less well at the extremes, both very lean and very high body fat.
Its main limitations are that it assumes a particular relationship between circumference measurements and fat distribution that does not hold equally across all body shapes. Men who carry fat differently - more viscerally versus subcutaneously, or with unusual proportions between neck and waist - will see larger errors.
Its main strengths are that it requires only a tape measure, it is reproducible when measurements are taken consistently, and it is far more accessible than DEXA, hydrostatic weighing, or Bod Pod testing. For tracking change over time it is genuinely useful - if your waist decreases and your neck holds steady, the formula will register a reduction in body fat regardless of whether the absolute figure was precisely accurate to begin with. Tracking the trend matters more than trusting the number on any single measurement.
If you have access to a BIA reading from smart scales, comparing it to the Navy method figure as this calculator does gives you a rough sense of how closely two imperfect methods agree. Strong agreement between them - within 3% - gives you more confidence in the working figure. A larger gap is a signal to weight the result loosely and focus on the trend over time rather than the absolute value.