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About this tool
Lean bulk calories from Mifflin-St Jeor maintenance, a training-level gain rate and protein, fat and carb targets.
Muscle Gain Calorie Calculator works the surplus backwards from the rate of weight gain you actually want, instead of guessing at a round number. Maintenance comes from the Mifflin-St Jeor equation multiplied by an activity factor; the target rate is set as a percentage of body weight per month — roughly 1 to 1.5 percent for beginners, 0.5 to 1 percent for intermediates and 0.25 to 0.5 percent for advanced lifters — and converted to daily calories using the 7,700 kcal per kilogram equivalence. It then splits the total into protein, fat and carbohydrate targets.
Open Muscle Gain Calorie Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
The surplus follows from the gain rate you choose, so it scales with body weight.
Mifflin-St Jeor for RMR, standard activity multipliers and Atwater factors for the macros.
Warns when the surplus is inside measurement noise or large enough that fat gain will outpace muscle.
Usually 5 to 20 percent above maintenance, which for most people is a surplus of about 150 to 500 kcal a day. The right number depends on your body weight and training age: a 75 kg intermediate targeting 0.75 percent gain a month needs only around 140 kcal a day extra.
About 1 to 1.5 percent of body weight a month for beginners, 0.5 to 1 percent for intermediates and 0.25 to 0.5 percent for advanced lifters. Gaining faster than that adds fat rather than extra muscle, because the rate at which muscle can be built is capped by training age.
Between 1.6 and 2.2 g per kilogram of body weight per day. A 2018 meta-analysis in the British Journal of Sports Medicine found resistance-training gains plateaued at about 1.62 g/kg, so the higher end is insurance rather than a requirement.
For most trained lifters, yes — a small surplus supports recovery and growth. Beginners, people returning after a break and those with higher body fat can gain some muscle at maintenance or in a deficit, which is why the tool lets you set a very low target rate. This is general fitness information, not dietary advice.
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