About

Standard bulking often leads to unnecessary fat accumulation. This calculator utilizes a Nutrient Partitioning strategy, specifically Carbohydrate Cycling, to direct nutrients where they are needed most. By undulating caloric intake between training and rest days, you maximize anabolic signalling when muscle tissue is damaged and maximize fat oxidation when sedentary.

This tool is designed for intermediate to advanced trainees aiming for Body Recomposition (building muscle while maintaining or losing fat) or a Lean Bulk. It solves the problem of "spillover"—where excess calories on non-training days are stored as adipose tissue rather than glycogen.

Formulas

The core logic utilizes the Mifflin-St Jeor equation for Basal Metabolic Rate (BMR), adjusted for Activity Level (TDEE), and then modified by the Cycling Factor.

TDEE = BMR × Activity

For Workout Days, we apply an anabolic surplus:

Cal_work = TDEE × 1.15

For Rest Days, we apply a maintenance or slight deficit logic to improve insulin sensitivity:

Cal_rest = TDEE × 0.95

Reference Data

Nutrient	Workout Day Role	Rest Day Role	Timing Strategy
Protein	Muscle Repair (Anabolic)	Muscle Preservation (Anti-Catabolic)	Evenly spread every 3-4 hours.
Carbohydrates	Glycogen Replenishment	Background Energy Only	80% Peri-workout (Pre/Intra/Post).
Fats	Minimum Requirements	Hormonal Support & Satiety	Away from the workout window.
Total Calories	Surplus (+10-15%)	Maintenance/Deficit (-5%)	Higher on leg/back days.
Insulin	High (Spike desired)	Low (Baseline desired)	Control via carb source selection.
Fiber	Moderate (Digestion speed)	High (Satiety)	Vegetables & fibrous grains on rest days.
Water	Hydration & Transport	Detoxification	0.5-1.0L during training.
Creatine	ATP Regeneration	Saturation Maintenance	5g daily regardless of activity.
Sodium	Pump & Contraction	Fluid Balance	Higher pre-workout.

Frequently Asked Questions

Cycling carbohydrates aligns energy availability with energy expenditure. High carbs on workout days spike insulin (an anabolic hormone) to drive amino acids into muscles. Low carbs on rest days keep insulin low, facilitating fat oxidation and preventing fat storage.

This tool is optimized for 'Lean Gains'. If your goal is maximum weight gain regardless of body fat, a standard surplus calculator might be simpler. This tool requires adherence to daily fluctuations.

Shift your 'Workout Day' macros to start the night before or ensure the majority of your daily carbohydrates are consumed in the meals immediately following your session.

Ideally, protein remains relatively constant or increases slightly on rest days to improve satiety when calories are lower. This calculator keeps protein high on both days to ensure positive nitrogen balance.