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Science-based calculators and guides for building lean muscle. Protein targets, FFMI, bulk vs cut — optimised for natural muscle gain.
Muscle gain (hypertrophy) is the process of increasing skeletal muscle size and strength through progressive resistance training combined with adequate nutrition. According to a 2018 meta-analysis published in the British Journal of Sports Medicine covering 1,863 participants, muscle gain is maximised with protein intake of approximately 1.62g per kg body weight per day, combined with a consistent resistance training programme.
Natural muscle gain rates are significantly lower than many expect. Research by Lyle McDonald and other exercise scientists suggests beginners can gain approximately 1–1.5kg of lean muscle per month in optimal conditions, declining to 0.5–1kg/month for intermediate trainees and 0.25–0.5kg/month for advanced athletes.
Progressive overload is the most important principle — consistently increasing training stress over time. This can be done by adding weight, reps, sets, or reducing rest periods. Without progressive overload, muscle growth plateaus regardless of diet.
Caloric surplus: A modest calorie surplus of 200–300 kcal/day above TDEE provides the energy substrate needed for muscle building without excessive fat accumulation. Use our bulk vs cut calculator to determine your starting point.
Training provides the stimulus for muscle growth — nutrition provides the raw material. Without adequate protein and sufficient calories, resistance training produces little muscle growth regardless of how hard you train. A 2018 meta-analysis published in the British Journal of Sports Medicine — covering 49 studies and 1,863 participants — found that protein supplementation significantly increased lean mass gains from resistance training, with a ceiling effect at approximately 1.62g per kg body weight per day during a surplus.
Carbohydrates are equally important for muscle gain — not for building muscle directly, but for fuelling the high-intensity training sessions that provide the hypertrophy stimulus. Muscle glycogen (stored carbohydrate) is the primary fuel source during resistance training. Low glycogen impairs training performance, reducing the quality and volume of work that drives muscle growth.
Muscle is not built during training — it is built during recovery. Training creates microscopic damage to muscle fibres; sleep and rest allow the body to repair and grow them larger and stronger. Research consistently shows that adults who sleep under 6 hours per night have significantly lower rates of muscle protein synthesis than those sleeping 7–9 hours. Prioritising sleep is one of the highest-leverage actions for muscle gain, yet it is routinely undervalued compared to training and nutrition optimisation.
Use the calculators in this section to set your protein target, determine your calorie surplus, assess your current lean body mass, and find your realistic monthly muscle gain potential based on your training experience level.