Muscle Protein Synthesis Window Calculator
Calculate how many grams of protein you should consume per meal to maximally stimulate muscle protein synthesis, given your body weight, daily protein target, meal frequency, and workout timing. Use it when designing a meal plan for muscle growth.
About this calculator
Muscle protein synthesis (MPS) is triggered by the amino acid leucine reaching a threshold in the bloodstream — typically around 2–3 g per meal for most adults. Below this threshold, the anabolic signal is blunted regardless of total daily protein. The leucine threshold is estimated as body_weight_kg × 0.045, with a floor of 2.5 g. Because leucine comprises roughly 1/6.6 of a complete protein dose, the minimum effective protein per meal = leucine_threshold × 6.6. The formula takes the larger of this minimum or your daily protein divided equally across meals: Optimal Per Meal = max(daily_protein / meal_frequency, leucine_threshold × 6.6). A training-status multiplier then increases the dose — ×1.3 post-workout and ×1.15 on training days — reflecting elevated MPS sensitivity after resistance exercise.
How to use
Suppose you weigh 180 lbs (≈81.6 kg), target 180 g protein daily, eat 4 meals, and it is post-workout. Leucine threshold = max(2.5, 81.6 × 0.045) = max(2.5, 3.67) = 3.67 g. Minimum effective protein per meal = 3.67 × 6.6 ≈ 24.2 g. Base per meal from daily target = 180 / 4 = 45 g. Optimal per meal = max(45, 24.2) = 45 g. Post-workout multiplier = 1.3. Final recommendation = round(45 × 1.3) = 59 g per post-workout meal. The remaining three meals would use the rest-day multiplier (×1.0), suggesting ~45 g each.
Frequently asked questions
What is the leucine threshold and why does it matter for muscle growth?
Leucine is a branched-chain amino acid that acts as a molecular trigger for mTORC1, the primary signaling pathway that initiates muscle protein synthesis. Research suggests you need approximately 2.5–3.5 g of leucine per meal to fully activate this pathway — amounts below this threshold produce a blunted anabolic response even if your total daily protein is adequate. This is why spreading protein evenly across 3–5 meals is generally superior to consuming most of it in one or two large meals. High-leucine protein sources include whey, eggs, chicken, and beef.
How does post-workout timing affect how much protein you should eat per meal?
Resistance exercise increases muscle sensitivity to amino acids for approximately 24–48 hours, but the effect is most pronounced in the first 2–4 hours post-workout. During this window, MPS rates are elevated and the muscle is primed to use available amino acids for repair and growth. The calculator applies a 1.3× multiplier to the post-workout meal to reflect this heightened demand. Consuming 40–60 g of fast-digesting protein (e.g., whey shake plus a meal) in this window is supported by multiple meta-analyses as beneficial for hypertrophy.
Is it better to eat more meals per day to maximize muscle protein synthesis?
Distributing protein across 3–5 meals generally maximizes the number of MPS-stimulating events per day, but there are diminishing returns beyond that frequency. Each protein-containing meal triggers an MPS spike that lasts roughly 3–4 hours, after which a refractory period occurs where additional protein has limited extra benefit. Eating 6–8 very small meals does not proportionally increase MPS and may reduce the size of each dose below the leucine threshold. Most research supports 3–5 evenly spaced meals of 30–50 g protein as optimal for muscle-building goals.