Bulk vs Cut Calculator —
Which Phase Should You Be In?

The bulk-or-cut decision is fundamentally a body-fat-threshold question. Researcher and sports nutritionist Alan Aragon, along with Lyle McDonald’s body recomposition work, converge on a consistent set of thresholds that have become a practical standard in evidence-based fitness coaching. For men: body fat above 15% signals that bulking will produce disproportionate fat accumulation, so a cut is warranted first. Body fat below 10% means the hormonal and anabolic environment strongly favors muscle growth, and a calorie surplus is appropriate. The window between 10% and 15% is the recomp zone — the narrow range where simultaneous fat loss and muscle gain is genuinely achievable, especially for intermediate trainees. For women, the thresholds shift upward by roughly 7–10 percentage points to account for essential fat differences: cut above 25%, bulk below 18%.

The calorie targets follow straightforward energy balance math. For a bulk, a modest surplus of 300 kcal per day — roughly 2,100 kcal per week — is sufficient to support approximately 0.5 lb of lean mass gain per week in natural trainees. Larger surpluses do not produce proportionally more muscle; they produce more fat. For a cut, a deficit of 500 kcal per day — 3,500 kcal per week — corresponds to roughly 1 lb of fat loss per week, which is the maximum rate at which most people can lose fat without significant muscle loss, provided protein intake is adequate (1.6–2.2 g per kg of body weight, per Phillips & Van Loon, 2011).

This calculator estimates your Total Daily Energy Expenditure using the Katch-McArdle formula, which bases the calculation on lean body mass rather than total body weight. This is more accurate than standard Harris-Benedict for people who know their body fat percentage, because metabolically active tissue — not fat — drives resting energy expenditure. The formula is: BMR = 370 + (21.6 × LBM in kg), multiplied by a moderate activity factor of 1.55. If your actual activity level is lower or higher, adjust the output accordingly.