How fast can you build muscle, and how much is possible without drugs?

By Robert Robinson, founder of Neato Health · September 15, 2026 · 4 min read

Muscle comes slowly, and there is a ceiling on how much a body can carry without drugs. Here is the study that found it, what it means for a realistic goal, and why gaining faster mostly means gaining fat.

Fat loss has a speed limit set by muscle. Muscle gain has one set by biology, and it is much lower than the fitness industry implies. Understanding the limit is the difference between a bulk that builds muscle and one that builds a belly.

The ceiling: fat-free mass index

Muscle scales with height, so “how much muscle can a person carry” needs a measure that removes height. Fat-free mass index, FFMI, is lean mass in kilograms divided by height in meters squared, the same shape as BMI but for the part of you that is not fat.

In 1995, Kouri, Pope, Katz and Oliva measured the body composition of 157 male athletes, 83 of whom admitted to using anabolic steroids and 74 who had not. Among the non-users, FFMI topped out at about 25. Among the users it ran well past that. They also examined 20 Mr. America winners from the pre-steroid era, 1939 to 1959, and found their FFMI averaged 25.4, with the highest at 27.3. The consistent ceiling across both groups gave the paper its conclusion: an FFMI much above 25 is a reliable sign of drug use in men.

For women, less has been published, but the same logic and the available data put the natural ceiling around 21 to 22.

Where Neato’s build goals sit

Neato’s automatic build goal for someone who is underweight or wants to add muscle is not the ceiling. It is a healthy muscularity mark: FFMI 19 for men and 15.5 for women, which corresponds to a body that looks athletic without any assumption about years in the gym. The ceilings of 25 and 21 bound what the app will let you set as a goal, so an impossible target is never offered.

The body-fat guide covers the other axis: a build goal arrives a few body-fat points above where you start, because some fat gain comes with any real surplus, and the app plans for it rather than pretending it away.

How fast the muscle comes

There is no single study that reports “pounds of muscle per month” for the general population, but the trials in Morton’s 2018 meta-analysis give a picture. Across 49 studies of adults doing resistance training with adequate protein, the average gain in fat-free mass was on the order of a kilogram over a 6- to 12-week program, more for beginners and less for trained people. That is roughly a pound a month for a beginner in a good program with enough protein, and it falls with every year of training. An experienced natural lifter is doing well to add two or three pounds of muscle in a year.

Two things drive the rate, and the research is clear on both:

• Training volume. Schoenfeld, Ogborn and Krieger’s 2017 meta-analysis found a dose-response relationship: more weekly sets per muscle, more growth, with 10 or more sets per muscle per week producing meaningfully more than fewer than five. Muscle is built by the training; the surplus only permits it.
• Protein. Morton’s breakpoint is 1.6 grams per kilogram a day, and Neato’s default of 0.8 grams per pound sits just above it. The protein guide has the details.

Why Neato caps bulk rates at 0.35 percent a week

If a beginner can build about a pound of muscle a month, gaining four pounds a month means three of them are fat. Neato’s automatic bulk rate is capped at 0.35 percent of body weight per week, about 0.6 pounds a week for a 170-pound man, or 2.5 pounds a month, and it slows further as your FFMI approaches the ceiling, because the muscle side of the gain shrinks with training age. The cap keeps the fat share of a bulk modest enough that the following cut is short.

Helms, Aragon and Fitschen recommend a similar conservatism for natural lifters: a small surplus, slow weight gain, and monitoring of body composition rather than the scale alone, precisely because the scale cannot tell muscle from fat.

Reading your own progress

Because muscle gain is slow and the scale is noisy, the useful signals are indirect. Strength going up on the same lifts is the most reliable. Waist staying flat while weight rises is the second: if the waist grows in step with the scale, the gain is mostly fat and the surplus is too big. Neato’s Body tab tracks weight, body fat and waist together for this reason, and the waist guide explains how to take the measurement so it means something.

Patience is the practical skill. A bulk that adds six pounds of muscle and six of fat over a year, followed by a cut that removes the fat in eight weeks, ends with six pounds of muscle you did not have. That is what a good year looks like. Anything promising it in twelve weeks is promising fat.

Neato’s guides are general wellness information built from the published research cited above. They are not a diagnosis, treatment, or medical advice, and they don’t know your history. For decisions about your health, talk to your doctor.