Methods in plain language
How FitCalc Calculators Work
Understand what each result estimates, the formula behind it, and where its limitations begin.
Estimates, not exact measurements
FitCalc calculators turn a defined set of inputs into a mechanical result using a stated formula. Inputs are converted to canonical metric units internally, calculations retain unrounded values, and results are rounded only for display. Formula and component versions are recorded so changes can be tested against prior behavior.
These estimates are useful starting points, not medical diagnoses or guarantees. Real energy expenditure and body composition vary between people and across time.
Results, evidence, and recommendations
Calculated Result
A mechanical output produced by a stated equation.
Evidence-Based Range
A range supported by research or recognized guidance when the evidence supports expressing a range.
FitCalc Recommendation
A practical interpretation or preferred target chosen by FitCalc. Recommendations are identified as such rather than presented as universal scientific facts. Not every current calculator uses all three layers.
TDEE and Goal Plan
FitCalc estimates resting energy expenditure with the Mifflin–St Jeor equation, then multiplies it by the activity level selected by the user. The Goal Plan applies FitCalc's established calorie-adjustment and macro rules.
Mifflin–St Jeor v1; FitCalc Activity v1; FitCalc Goal Plan v1; FitCalc Macros v1
Adults ages 18–100 within the calculator's supported ranges.
A selected population-level activity multiplier can represent typical activity, and the result is a planning starting point.
Individual expenditure varies. Weekly pace uses the established static 3,500-calorie approximation.
Macro Calculator
FitCalc calculates or accepts daily calories, allocates its practical protein target first, allocates fat next, and gives carbohydrate the remaining energy.
FitCalc Macro v1
Fat loss -15%; maintenance 0%; muscle gain +10%.
Protein 2.2 g/kg; fat is the greater of 0.6 g/kg or about 25% of calories; carbohydrate is the remainder.
No split is uniquely correct. Low-calorie conflicts are shown explicitly.
Protein Calculator
The result separates a research-informed range from FitCalc's practical high-end recommendation.
FitCalc Protein v1
Resistance-training contexts use 1.6–2.2 g/kg/day; general contexts use lower goal-specific ranges.
Usually the high end—about 1 g/lb—clearly labeled as a preference, not a universal minimum.
Not pediatric, pregnancy/lactation, kidney-disease, or clinical nutrition guidance.
BMI
Body mass index compares weight with height squared and applies the established adult BMI categories. FitCalc uses it as a quick screening reference.
BMI Standard v1
Adults within the calculator's supported ranges.
BMI is used as a screening measure.
It does not distinguish fat mass from lean mass and is not a diagnosis.
Body Fat Percentage
FitCalc uses the sex-specific U.S. Navy circumference equations with height, neck, waist or abdomen, and hip measurements where required.
Navy Body Fat v1
Adults within the calculator's supported ranges.
Circumferences are measured consistently at the locations described.
Measurement technique affects the result. It is a field estimate, not a laboratory measurement or diagnosis.
Review and corrections
Methodology records include review dates. A date is updated when the relevant method or review changes, not merely because unrelated site code changes. If you find a formula, citation, or explanation that appears incorrect, please contact FitCalc.