Calorie, Fitness & Body Composition Simulation Engine

Model your BMR, TDEE, lean mass, fat mass, and weekly progress using evidence-based estimates. Choose general or athlete mode, set your calorie target, and see projected weight and physique changes over time. This tool is for education and planning — not medical advice.

Educational only · Not a medical diagnosis or prescription

Mode

General mode uses moderate protein and balanced macros.

Sex

Age (years)

Height

Feet and inches.

Weight (lbs)

Body fat % (estimate)

Activity level

Training days per week

Simulation length (weeks)

Goal

Daily calorie offset vs TDEE

Negative for deficit, positive for surplus. You can tweak later.

Override with fixed calories (optional)

Leave blank to use TDEE + offset.

Metabolism & daily targets

BMR (Mifflin–St Jeor)

0 kcal

TDEE (maintenance)

0 kcal

Chosen daily calories

0 kcal

Daily surplus/deficit

0 kcal

Starting lean mass

0 lb

Starting fat mass

0 lb

Physique score (0–100)

–

Physique score is a simple metric weighting body fat %, lean mass, and mode. Higher = leaner + more muscle.

Macro targets (training vs rest days)

Training: Protein / Carbs / Fat

–

Rest: Protein / Carbs / Fat

–

Protein grams per lb (mode)

–

Athlete mode shifts more calories into protein and carbs on training days and slightly raises total intake.

12-Week Body Composition Projection

This model assumes ~3,500 kcal per pound of fat, modest lean-mass adaptations, and slightly more favorable composition changes in athlete mode. Real-world results vary with genetics, training quality, sleep, and adherence.

Weekly projections

Week	Weight	Body fat %	Lean mass	Fat mass	Weekly kcal Δ	Physique change
Enter your details and run the simulation to see week-by-week projections.

Weekly physique change is relative to week 0 based on lean mass and body fat %.

Important notes

This engine provides estimates only and is not a substitute for medical or nutritional advice.
Rapid weight loss, extreme deficits, and long-term very low-calorie diets can be harmful.
Consult a qualified professional before making major changes to your diet or training.
All calculations are approximate and depend on the accuracy of your inputs.

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