Natty or Not Calculator
Estimate how your current muscularity compares to frame-adjusted natural FFMI limits.
Mass and leanness are comfortably inside typical natural limits for your frame.
Positive values mean your current body weight is above the model's frame-adjusted ceiling at your selected body-fat percentage.
| FRAME | NFFMI LIMIT |
|---|---|
Small Frame | 24.4 |
Medium Frame | 25 |
Large Frame | 25.6 |
Natty or Not Interpretation
This score compares your normalized FFMI against a frame-adjusted natural ceiling. It is a screening model, not proof of PED use.
| RANGE | CATEGORY |
|---|---|
| 0-90 | Very Likely Natural Mass and leanness are comfortably inside typical natural limits for your frame. |
| 90-98 | Likely Natural Still within realistic natural range, especially with consistent training history. |
| 98-104 | Advanced Natural Range Near the upper natural ceiling where genetics, measurement quality, and context matter more. |
| 104-110 | Gray Zone Above common natural ceilings. Re-check body-fat input, height, and body-weight data first. |
| 110-120 | Unlikely Natural Muscularity is above typical frame-adjusted natural limits in most datasets. |
| 120+ | Highly Unlikely Natural Far above usual natural ceilings. This is a screening signal, not proof of PED use. |
What This Natty or Not Calculator Does
This tool is a practical screening model for gym users who want to estimate whether a physique sits inside or outside typical natural muscularity limits. It uses normalized FFMI as the core metric, then adjusts the ceiling by frame size using wrist-to-height context.
It does not diagnose steroid use and it should never be used to accuse someone. It is best used for self-audit and reality-checking your own progress expectations.
How The Score Works
The model combines three steps:
- Estimate lean mass from body weight and body-fat percentage.
- Calculate FFMI and normalized FFMI from lean mass and height.
- Adjust the natural ceiling by frame size (small, medium, large) and compare against it.
FFMI = Lean Mass (kg) / Height(m)^2
Normalized FFMI = FFMI + 6.3 x (1.8 - Height in meters)
Natty Score = (Normalized FFMI / Frame-Adjusted Natural Limit) x 100
If you want to isolate the FFMI part without the frame adjustment, use the FFMI Calculator. If you want to verify the frame context directly, use the Body Frame Size Calculator.
How To Interpret Your Result
A higher score means your current muscularity is closer to, or above, a frame-adjusted natural ceiling. Scores in the upper natural and gray-zone bands are highly sensitive to data quality, especially body-fat input.
The easiest way to reduce false alarms is to keep measurement conditions consistent: same scale, same time of day, similar hydration, and repeatable body-fat method.
Important Limitations
This is a heuristic, not a lab test. False positives can happen when body-fat is underestimated, height is rounded down, or photos create unrealistic body-fat assumptions.
Genetics, training age, and sport history matter. A very advanced natural athlete may appear in upper bands, while someone with poor data quality may look suspicious by mistake.
For better context, pair this with the Lean Body Mass Calculator and Muscle Mass Calculator. If body-fat is uncertain, cross-check with the Body Fat Calculator or photo-based body-fat estimator.
For a dedicated ceiling-utilization model with stage projections, use the Muscular Potential Calculator.
For a combined structure-plus-potential composite score, compare with the Bodybuilding Genetics Calculator.
PED Context and Health Risk
Anabolic-androgenic steroid use is associated with meaningful cardiovascular and systemic risk. Even when physique outcomes look impressive, long-term health costs can be severe.
This tool exists to set realistic natural expectations and reduce comparison bias, not to encourage or normalize PED use.
References
- Kouri EM, et al. Fat-free mass index in users and nonusers of anabolic-androgenic steroids.PubMed record
- Cintineo HP, et al. Sport differences in fat-free mass index in the NCAA.PubMed record
- Esco MR, et al. Normative fat-free mass index values for female collegiate athletes.PubMed record
- NIDA. Anabolic steroids and other appearance and performance enhancing drugs.NIDA overview
- Baggish AL, et al. Cardiovascular toxicity of illicit anabolic-androgenic steroid use.PubMed record
- Sessa F, et al. Anabolic-androgenic steroid use and cardiovascular disease.PubMed record
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