Calculation Method

Scope

The calculator is intended for healthy adults who perform resistance training and have maintenance, hypertrophy, fat-loss, or recomposition goals.

It is not intended for kidney disease, pregnancy, adolescents, eating disorders, clinical nutrition, diagnosed medical conditions, geriatric nutrition, medically supervised weight loss, or endurance-sport planning.

Unit Handling

Protein research is usually expressed as grams of protein per kilogram of body weight per day. Inputs are converted to kilograms internally before applying the evidence-based multipliers.

• Metric users see kilograms first, with pounds in parentheses.
• Imperial users see pounds first, with kilograms in parentheses.

When the unit system is switched, valid height, current body weight, and known lean body mass values are converted into the newly selected unit fields. Body-fat percentage, target body-fat percentage, goal, diet phase, training frequency, meals per day, and lean-mass source labels are not changed by the unit switch.

If the converted fields already contain equivalent values from a previous switch, the calculator preserves those values when switching back. This prevents visible round-trip drift from unit-conversion rounding while keeping the scientific calculation in kilograms.

Body-Composition Estimates

The calculator always estimates BMI:

BMI = weightKg/(heightM * heightM)

If body-fat percentage is supplied, it estimates fat mass and lean body mass:

fatMassKg = weightKg * (bodyFatPercent/100)
leanBodyMassKg = weightKg - fatMassKg

If known lean body mass or fat-free mass is supplied from a body-composition assessment, the calculator uses that value before the body-fat-percentage estimate for lean-mass-adjusted calculations:

leanBodyMassKg = suppliedLeanBodyMassKg
fatMassKg = weightKg - suppliedLeanBodyMassKg
bodyFatPercentUsed = fatMassKg/weightKg * 100

The supplied value must be lower than current body weight and must imply a body-fat percentage between 3% and 70%. If body-fat percentage and known lean body mass conflict materially, the calculator warns the user and uses the supplied lean-mass value for adjusted calculations.

For fat-loss and recomposition goals only, if target body-fat percentage is supplied, the calculator estimates goal weight while assuming lean mass is preserved:

goalWeightKg = leanBodyMassKg/(1 - targetBodyFatPercent/100)

This goal-weight estimate is not a prediction. It is only a simplified body-composition estimate.

For fat loss, target body-fat percentage must be lower than current body-fat percentage. For recomposition, a target body-fat percentage that is equal to or higher than current body-fat percentage is not used for the goal-weight branch; the calculator falls back to the lean-mass-adjusted recomposition basis.

Target body-fat percentage is not used for maintenance or muscle gain in version 1. Maintenance uses current body weight. Muscle gain/bulking would also need target body weight, projected lean-mass gain, or an expected fat:lean gain split before target body fat could drive a protein estimate.

Protein Recommendation Model

Protein values are calculated raw first, then rounded to the nearest 5 grams for display. The default target is the midpoint of the raw practical range before rounding.

The result view also reports method sensitivity by comparing the rounded midpoint targets from the available current-weight, lean-mass, and goal-weight estimates. The spread is labeled as same-result, small, moderate, or large so users can see whether body-composition and goal-weight assumptions materially change the recommendation.

Maintenance

minimum = weightKg * 1.4
rangeLow = weightKg * 1.6
rangeHigh = weightKg * 2.0

If body-fat percentage is supplied, the calculator still shows fat mass, lean body mass, and lean-mass context. The selected maintenance target remains current-body-weight based.

Target body-fat percentage is not shown or used for maintenance because a changed body-fat target implies a body-composition change rather than maintenance.

Muscle Gain/Hypertrophy

minimum = weightKg * 1.6
rangeLow = weightKg * 1.6
rangeHigh = weightKg * 2.2

If body-fat percentage is supplied, the calculator shows lean-mass context for interpretation. The selected hypertrophy target remains current-body-weight based.

Target body-fat percentage is not used for muscle gain in version 1. Bulking can include fat gain, but target body fat alone does not define future lean mass or final body weight.

Fat Loss And Recomposition

Fat-loss and recomposition goals use both goal and diet phase intensity. Fat loss is modeled with a stronger lean-retention bias. Recomposition is modeled slightly lower because the goal includes resistance-training adaptation and is usually closer to maintenance or a smaller deficit.

If target body-fat percentage is supplied for a valid fat-loss or recomposition goal-weight estimate, the adjusted basis is estimated goal weight. Otherwise, the adjusted basis is lean body mass.

If known lean body mass is supplied, it is used as the lean-mass basis for these modes. DXA, BIA, skinfold/caliper, and other body-composition methods can differ and are sensitive to protocol, hydration, recent training, and device equations, so this value is still treated as an estimate.

The optional lean-mass source selector is for reporting and interpretation only. It records whether the supplied value came from DXA/DXA, BIA, skinfold/caliper assessment, or another method. If "other measured estimate" is selected, the user can optionally enter a custom name for that source. The source label and custom name do not change the formula or multipliers. Only the supplied lean-mass number changes the calculation.

Fat Loss: Moderate Deficit

minimum = max(leanBodyMassKg * 2.0, adjustedBasisKg * 1.6)
rangeLow = max(leanBodyMassKg * 2.1, adjustedBasisKg * 1.8)
rangeHigh = max(leanBodyMassKg * 2.3, adjustedBasisKg * 2.0)

Fat Loss: Aggressive Cut/Lean Athlete Context

minimum = max(leanBodyMassKg * 2.3, adjustedBasisKg * 1.8)
rangeLow = max(leanBodyMassKg * 2.3, adjustedBasisKg * 2.0)
rangeHigh = max(leanBodyMassKg * 3.1, adjustedBasisKg * 2.2)

Recomposition: Maintenance/Slight Deficit

minimum = max(leanBodyMassKg * 1.8, adjustedBasisKg * 1.5)
rangeLow = max(leanBodyMassKg * 1.9, adjustedBasisKg * 1.6)
rangeHigh = max(leanBodyMassKg * 2.2, adjustedBasisKg * 1.8)

Recomposition: Moderate Deficit

minimum = max(leanBodyMassKg * 1.9, adjustedBasisKg * 1.6)
rangeLow = max(leanBodyMassKg * 2.0, adjustedBasisKg * 1.7)
rangeHigh = max(leanBodyMassKg * 2.3, adjustedBasisKg * 1.9)

If neither body-fat percentage nor known lean body mass is supplied, the calculator uses a reduced-precision current-weight fallback. Body-composition input is especially important for aggressive cutting because that model is based on lean-mass scaling.

fat loss, moderate deficit:
minimum = weightKg * 1.6
rangeLow = weightKg * 1.7
rangeHigh = weightKg * 2.0

fat loss, aggressive cut/lean athlete:
minimum = weightKg * 1.8
rangeLow = weightKg * 2.0
rangeHigh = weightKg * 2.4

recomposition, maintenance/slight deficit:
minimum = weightKg * 1.5
rangeLow = weightKg * 1.6
rangeHigh = weightKg * 2.0

recomposition, moderate deficit:
minimum = weightKg * 1.6
rangeLow = weightKg * 1.7
rangeHigh = weightKg * 2.0

Per-Meal Distribution

perMealProtein = defaultTarget/mealsPerDay

Per-meal output is a distribution aid. Total daily protein remains the main recommendation.

Limits Of The Estimate

• User-entered body-fat percentage may come from an imprecise external estimate.
• Lean body mass is either supplied from an external body-composition estimate or calculated from the entered body-fat percentage; it is not independently measured by this calculator.
• User-supplied lean body mass can differ across DXA, BIA, skinfold/caliper, and other methods.
• Goal-weight estimates assume lean mass is preserved.
• The calculator does not know actual calorie intake or deficit size.
• Training frequency is a rough proxy for training volume and quality.
• Protein quality, digestibility, leucine content, and dietary pattern are not directly modeled.

Evidence Basis

The model is based on sports-nutrition position stands, systematic reviews, meta-analyses, and trials relevant to resistance training, lean-mass retention, and protein distribution.

• Citation: Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., Purpura, M., Ziegenfuss, T. N., Ferrando, A. A., Arent, S. M., Smith-Ryan, A. E., Stout, J. R., Arciero, P. J., Ormsbee, M. J., Taylor, L. W., Wilborn, C. D., Kalman, D. S., Kreider, R. B., Willoughby, D. S., ... Antonio, J. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, Article 20. https://doi.org/10.1186/s12970-017-0177-8

  Use in calculator: Broad resistance-training protein range.

• Citation: Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., Aragon, A. A., Devries, M. C., Banfield, L., Krieger, J. W., & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), 376-384. https://doi.org/10.1136/bjsports-2017-097608

  Use in calculator: 1.6 g/kg/day hypertrophy anchor.

• Citation: Iraki, J., Fitschen, P., Espinar, S., & Helms, E. (2019). Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports, 7(7), Article 154. https://doi.org/10.3390/sports7070154

  Use in calculator: Muscle-gain/bulking context, including controlled surplus, weight-gain rate, and body-composition monitoring.

• Citation: Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11, Article 20. https://doi.org/10.1186/1550-2783-11-20

  Use in calculator: Lean-athlete cutting context, applied cautiously.

• Citation: Helms, E. R., Zinn, C., Rowlands, D. S., & Brown, S. R. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2), 127-138. https://doi.org/10.1123/ijsnem.2013-0054

  Use in calculator: Lean-mass scaling during caloric restriction.

• Citation: Mettler, S., Mitchell, N., & Tipton, K. D. (2010). Increased protein intake reduces lean body mass loss during weight loss in athletes. Medicine & Science in Sports & Exercise, 42(2), 326-337. https://doi.org/10.1249/MSS.0b013e3181b2ef8e

  Use in calculator: Higher protein during energy restriction.

• Citation: Longland, T. M., Oikawa, S. Y., Mitchell, C. J., Devries, M. C., & Phillips, S. M. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. American Journal of Clinical Nutrition, 103(3), 738-746. https://doi.org/10.3945/ajcn.115.119339

  Use in calculator: Recomposition and fat-loss context.

• Citation: Refalo, M. C., Trexler, E. T., & Helms, E. R. (2025). Effect of dietary protein on fat-free mass in energy restricted, resistance-trained individuals: An updated systematic review with meta-regression. Strength and Conditioning Journal. https://doi.org/10.1519/SSC.0000000000000888

  Use in calculator: Fat-free-mass scaling during energy restriction, with heterogeneity caveats.

• Citation: Kasper, A. M., Langan-Evans, C., Hudson, J. F., et al. (2021). Come back skinfolds, all is forgiven: A narrative review of the efficacy of common body composition methods in applied sports practice. Nutrients, 13(4), 1075. https://doi.org/10.3390/nu13041075

  Use in calculator: Measurement-method caveats for DXA, BIA, and skinfold/caliper-derived estimates.

• Citation: Schoenfeld, B. J., & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15, Article 10. https://doi.org/10.1186/s12970-018-0215-1

  Use in calculator: Per-meal distribution context.