Free tool
Natural muscle potential calculator
No formula can tell you your genetic ceiling. What exists is FFMI data: in Kouri et al. (1995), the normalized FFMI of 74 male athletes who did not use steroids extended up to a limit of about 25.0. This calculator translates those levels into kilograms of lean mass at your height — and, if you add your current numbers, shows how far you are from each.
What this number is not
It isn't your genetic limit, it isn't a goal, and it isn't a steroid test. The reference study was small, male-only, relied on self-reported drug use, and its own authors called the findings preliminary. A 3-point error in your body fat estimate moves FFMI by close to a full point.
Your trend matters more than the ceiling
An FFMI that climbs slowly over months tells you more than any comparison with a theoretical maximum. Corpus estimates body fat and normalized FFMI at every photo check-in, so you can follow that trend without redoing the math.
Common questions
What is the natural limit for FFMI?
The most-cited figure comes from Kouri et al. (1995): among 74 male athletes who didn't use steroids, normalized FFMI extended up to a limit of about 25.0, and Mr. America winners from the pre-steroid era had an estimated average of 25.4. It's a small, male-only study based on self-reported drug use — a reference point, not a biological rule.
How much muscle can I gain naturally?
There is no reliable individual formula. Gains are usually fastest in the first years of training and slow down after that. The lean-mass gap to each FFMI level gives a sense of scale, but the useful signal is your own trend over months.
Does this apply to women?
The math works for anyone, but the reference levels come from male samples. There's no widely validated female reference, so treat the table rows as mathematical comparison points only.
Why do I need my body fat percentage?
FFMI is built on fat-free mass, which depends on the body fat percentage you enter. Any error in that estimate carries straight into the result — which is why using the same measurement method every time matters.
Is an FFMI above 25 proof of steroid use?
No. The study authors proposed FFMI only as an initial screening idea, and ordinary body-fat estimation error can move FFMI by close to a point. A high value on its own proves nothing about anyone.