Forty-nine studies. 1,863 people. The pooled answer to how much muscle you can gain in a month: about three-quarters of a pound from training alone. Closer to one pound if your protein is dialed in.
Except the variation between people was wider than the average itself. Some gained barely anything. Others gained more than double. Same kinds of programs. Same timeframes. The "average" tells you what happened to no one in particular.
What actually determines your number comes down to a few variables — and the one most people obsess over contributes the least.
How much muscle can you gain in a month, according to the data
A meta-analysis of 49 resistance training studies found participants gained about 1.1 kg of lean mass over 13 weeks from training alone — roughly 0.34 kg per month. Optimal protein supplementation brought the total to about 0.43 kg per month, under one pound.
— Morton et al. 2018 · British Journal of Sports Medicine · n=1,863
Here is the part every other article about monthly muscle gain leaves out. Training itself drives about 91% of the muscle you gain. Protein adds about 9%.
Over three months, training alone built 1.1 kg of lean mass. Protein supplementation added 0.30 kg on top. That is the entire gap between supplementing and not — less than the weight of a tennis ball per month.
Yet most people chasing muscle spend enormous mental energy on protein. Grams per meal. Timing windows. Powder versus whole food. The meta-analysis found that none of those details significantly changed the outcome. Total daily intake mattered. Whether you actually trained mattered. The rest was noise.
The protein ceiling: about 1.6 grams per kilogram of bodyweight per day. For someone weighing 75 kg, that is roughly 120 grams. If you are already there, another shake changes nothing.
But two other variables shift your personal number far more than supplementation ever could.
Age. People under 45 saw a meaningful protein boost — about half a kilogram of extra lean mass. People over 45 saw essentially nothing. The gap between groups was large enough that random chance is ruled out. If you are over 40 and your expectations come from advice written for twenty-something lifters, you are measuring yourself against a benchmark that does not apply to your body.
Training drives 91% of your muscle gain. Protein — the variable most people pour money and attention into — adds 9%.
Training history. This one flips what most people expect. Experienced lifters got seven times more lean mass from extra protein than untrained beginners. Your body gets better at using protein the longer you have been training. Beginners grow from the training signal alone, regardless of how carefully they time their shakes.
And training volume determines how strong that signal is. A separate 67-study analysis found that every additional weekly set per muscle group produced more growth — but with diminishing returns. The minimum for detectable growth: about 4 sets per muscle group per week. The sweet spot: 5 to 10.
One number that tends to get buried: people who supplemented protein lost nearly a pound of body fat while gaining lean mass. Total body weight barely moved. If you are watching the scale and seeing nothing change despite consistent training, your body may be doing exactly what the data predicts — quietly trading fat for muscle at a pace a bathroom scale will never catch.
The actual range — somewhere between barely anything and well over a pound per month — depends on your age, your training volume, and your history. Protein matters — but only up to a ceiling. And only as the 9% addition to the 91% that training already provides.
And if a break from training ever makes you worry about losing what you have built, the data says your muscles remember more than you would expect.
And if training drives 91% of the result, the next step isn't in the supplement aisle — it's understanding how much volume is enough, and where more stops helping.