CalorieCalcTools editorial team · Published 2026-06-30
A lean bulk means eating 10 to 20 percent above maintenance, roughly 250 to 500 calories a day for most lifters, with protein set at 1.6 to 2.2 grams per kilogram of body weight. That combination, drawn from the International Society of Sports Nutrition's position stands on protein and on diets and body composition, is what separates a bulk that builds muscle from one that mostly builds a bigger waistband.
Why the surplus size matters
Muscle protein synthesis has a ceiling. The body can only repair and build new tissue so fast, and no amount of extra food pushes past that ceiling faster, according to Eric Helms, Alan Aragon and Peter Fitschen's evidence-based bodybuilding nutrition guidelines, published in the Journal of the International Society of Sports Nutrition. Calories beyond what muscle-building requires get stored as fat instead. Their recommendation for the off-season bulking phase is a surplus of roughly 10 to 20 percent above maintenance calories, with novice and intermediate lifters landing on the higher end of that range and more experienced lifters pulling back toward the lower end.
The ISSN's separate position stand on diets and body composition puts a finer point on it: research comparing surplus sizes consistently finds that larger surpluses mostly add fat, not muscle. A 300-calorie surplus and a 1,000-calorie surplus do not build muscle at different speeds; the muscle-building rate stays capped by biology. The extra calories in the bigger surplus just go somewhere else.
Why dirty bulks backfire
The old advice to "eat big to get big" ignores that ceiling entirely. A dirty bulk (eating well past maintenance with little regard for food quality or macro targets) tends to add fat at two to three times the rate of a measured surplus, without a matching increase in muscle. The fat has to come off eventually, which means a longer cut later, more total time spent restricting calories, and in some cases enough fat gain to affect insulin sensitivity and make the next cut harder than it needed to be. A slower, tracked surplus costs a little patience up front and saves months of cleanup later.
Setting protein, then carbs and fat
The ISSN's protein position stand, led by Ralf Jäger and colleagues, sets the effective range for building muscle at 1.6 to 2.2 grams of protein per kilogram of body weight per day, or roughly 0.7 to 1 gram per pound. That is well above the basic RDA of 0.8 g/kg, which is a floor set to prevent deficiency in sedentary adults, not a target for anyone training with any regularity. This calculator sets protein first, then splits the remaining calories between carbs and fat, holding fat at a share high enough to support hormone production and keep meals from feeling austere.
Worked example
Take a 28-year-old man, 5'9", 160 lb, moderately active (training 3 to 5 days a week), running a standard +15 percent bulk.
Mifflin-St Jeor BMR: (10 × 72.6 kg) + (6.25 × 175.3 cm) - (5 × 28) + 5 = 726 + 1,096 - 140 + 5 ≈ 1,687 calories.
TDEE: 1,687 × 1.55 (moderate activity) ≈ 2,615 calories.
Bulking target: 2,615 × 1.15 ≈ 3,007 calories, rounded to about 3,010.
Protein at 0.9 g/lb (inside the ISSN's 0.7 to 1 g/lb range): 144 g (576 calories). Fat at roughly 25 percent of total calories: about 84 g (752 calories). The remainder, about 1,679 calories, becomes carbs: roughly 420 g.
Expected gain at this surplus and activity level: about 1 to 2 percent of body weight per month, or roughly 1.6 to 3.2 lb, assuming consistent training and protein intake.
The Mifflin-St Jeor equation is the formula behind that BMR figure. A systematic review published in the Journal of the American Dietetic Association found it predicted resting metabolic rate more accurately than other commonly used equations in both non-obese and obese adults, which is why it is the standard starting point here and across this site's other calorie calculators.
Limitations
Every number above is an estimate built from population averages. Individual metabolic rate varies by several percent even among people matched for age, sex, height and weight, and the calculator has no way to see your actual training history, sleep, stress or genetics, all of which affect how a surplus gets used. Treat the calorie and macro numbers as a starting point, track your actual weight trend over 3 to 4 weeks, and adjust the surplus up or down based on what the scale and the mirror show rather than sticking rigidly to a formula. Anyone with a diagnosed eating disorder, a metabolic condition, or other medical concerns should work with a doctor or registered dietitian instead of relying on a calculator.
Not bulking? Try the standard macro calculator
If you are cutting or maintaining instead, the general macro calculator covers balanced, high-protein, low-carb and keto splits.