Stop Guessing.
Start with a Strategy.
BodyCompOS maps your body fat, training age, and goals to a science-backed phase recommendation — with calorie targets, protein ranges, and a real timeline. 100% private, no account needed.
Interactive Engine
Strategy Finder
Your strategy appears here
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The BodyCompOS Loop
A System, Not Just a Calculator
Most fitness tools give you a number and stop. BodyCompOS connects assessment, targeting, tracking, and intelligent reassessment into one coherent strategy loop.
Assess
Your stats & body composition
Analyze
Algorithm weighs all inputs
Recommend
Personalized phase direction
Track
Weekly check-ins & forecast
Improve
Reassess & adjust targets
Strategy Recommendation
Cut, lean bulk, recomp, or maintain — with confidence score and alternative pathway.
19 Precision Calculators
TDEE, BMR, FFMI, protein, macros, body fat, lean mass, ideal weight, and more.
Evidence-Based Guides
Cut vs bulk, body recomposition, protein science, body fat measurement — ISSN cited.
Strategy Comparisons
Cut vs recomp, lean bulk vs aggressive bulk, BMI vs body fat — side-by-side.
Progress Tracker
Weekly check-ins, adherence scoring, plateau detection, and metabolic forecast.
Peer-Reviewed Methodology
Every formula cited. Mifflin-St Jeor, Navy Method, Kouri 1995, ISSN protein stands.
Operating Loop
From assessment to reassessment
BodyCompOS links assessments with strategy guidance, calorie setting, and progressive monitoring to answer: is your strategy actually working?
Assessment
Enter sex, age, height, weight, activity levels, and lifting background to define your physical base.
Strategy Choice
Identify your optimal current strategy (cut, bulk, maintenance, or recomp) and view confidence levels.
Calorie & Protein Targets
Get personalized starting nutrition targets using conservative metabolic rate formulas.
Weekly Check-Ins
Log daily weigh-ins and tracking adherence percentages locally without uploading sensitive data.
Progress Forecasting
Let the local forecast engine estimate your weeks-to-target weight and rate of change.
Trend Reassessment
Compare actual rates of change against predicted progress and adjust calorie targets automatically.
Calculators
Supporting Strategy Tools
Dive deeper into custom metrics, formula breakdowns, and biological indexes once you have defined your primary direction.
TDEE Calculator
Estimate Total Daily Energy Expenditure and maintenance calories using Mifflin-St Jeor BMR, refined with Katch-McArdle when body fat is available. Activity multipliers range from sedentary (1.2) to competitive (1.9). TDEE is the foundation for calorie planning, fat loss, and lean bulk targets.
Calorie Calculator
Calculate daily calorie targets for fat loss (cutting at 85% TDEE), lean bulk (108%), aggressive bulk (115%), or recomposition (98%). Conservative multipliers optimize fat mobilization while preserving muscle mass. A practical starting point for body composition strategy planning.
Protein Calculator
Estimate daily protein intake for muscle protein synthesis, fat loss, and lean mass retention. Based on ISSN guidelines: 1.6-2.2 g/kg body weight adjusted by goal. Higher end (2.2 g/kg) recommended during calorie deficit to prevent muscle catabolism.
Goal Timeline Calculator
Forecast timeline to reach target body weight using compounding metabolic decay rather than linear projection. Accounts for metabolic adaptation with conservative weekly rates: 0.75% for fat loss, 0.2-0.4% for muscle gain. Generates non-linear projection curves for realistic planning.
Body Fat Calculator
Estimate body fat percentage using the US Navy Circumference Method. Uses neck, waist, and hip measurements with sex-specific logarithmic formulas. Outputs body fat percentage, lean mass, and fat mass for body composition assessment and strategy selection.
FFMI Calculator
Calculate Fat-Free Mass Index (FFMI) to quantify muscle mass relative to height. Uses raw FFMI with Kouri height normalization to correct tall-athlete skew. Provides body composition context beyond BMI for training and strategy planning.
Trust Foundations
Transparent calculations, local privacy
Formulas shown, tracking stays local, editorial policy in place. No fabricated claims, no server uploads.