Medical & Fitness Disclaimer
Last updated: 2026-07-07
FFMI Check exists to make peer-reviewed fitness math easier to run. It does not exist to replace a doctor, dietitian, coach, or physiotherapist. Please read the whole page before making training or nutrition decisions based on anything you calculate here.
Educational use only
All calculators, articles, comparison tables, and reference values on this site are provided for educational and informational purposes only. They are not medical, nutritional, or professional fitness advice. They are not a substitute for consultation with a qualified healthcare provider.
Do not use FFMI Check to:
- Diagnose or treat any medical condition
- Design a rehabilitation program after injury
- Manage a chronic condition (diabetes, cardiovascular disease, thyroid disorder, etc.)
- Plan nutrition during pregnancy, lactation, or eating disorder recovery
- Make training decisions for children or adolescents without professional oversight
Accuracy has limits
Every formula on FFMI Check comes with documented accuracy bounds from the source research. In plain terms:
- FFMI depends on an accurate body fat estimate. A 3-point error in body fat moves FFMI by ~1.5 units.
- TDEE using Mifflin-St Jeor is accurate within ±10% for ~82% of healthy adults. It can be significantly off for very muscular, obese, older, or thyroid-affected people.
- US Navy body fat method has ±3–4% accuracy vs DEXA in healthy adults. Higher error at the extremes.
- 1RM estimation with Epley and Brzycki formulas is most accurate at 1–10 reps and degrades above that.
Individual results vary significantly. Treat calculator output as a starting hypothesis, not a diagnosis.
Consult a professional
Consult a qualified professional (physician, registered dietitian, certified strength and conditioning specialist) before:
- Starting an aggressive calorie deficit or bulk
- Adding significant new training volume, especially with prior injury
- Interpreting body composition changes in the context of your health history
- Making decisions during pregnancy, adolescence, or older age
No liability
FFMI Check, its authors, and its operators assume no responsibility for any injury, illness, or adverse outcome resulting from your use of the site or reliance on any calculator or article. You use the information at your own risk.