What This Calculator Measures

Relative Energy Deficiency in Sport describes what happens when an athlete's dietary energy intake fails to cover the cost of training alongside normal physiological function. The central quantity is energy availability: intake minus exercise energy expenditure, divided by fat-free mass, in kilocalories per kilogram of fat-free mass per day. Fat-free mass is the denominator because metabolically active tissue, not total body weight, determines the requirement. Roughly 45 kcal/kg FFM per day is considered optimal, 30 to 45 is a reduced state where adaptations begin, and below 30 is clinically low — the point at which research consistently shows suppressed luteinising hormone pulsatility, falling bone formation markers and measurable endocrine disruption.

Why the Score Includes More Than Energy

Energy availability alone is a snapshot, and self-reported intake is systematically underestimated. The risk score therefore combines it with the indicators clinicians actually weigh: body mass index, menstrual function in female athletes, the number of prior bone stress injuries, and a screen for disordered eating behaviour. Each contributes points, and no single factor is allowed to dominate the total. The resulting tier maps to the traffic-light logic used in sports medicine — green for full participation with monitoring, amber for supervised training with medical review, red for withholding from competition pending treatment.

Male Athletes Are Routinely Missed

The model that preceded RED-S, the Female Athlete Triad, framed the problem as a women's issue. Male athletes experience the same deficiency but lack the visible signal of menstrual disturbance, so presentation is delayed and arrives instead as reduced testosterone, low bone mineral density, recurrent stress fractures, frequent illness and performance that stops improving despite increased training. Reported prevalence is highest in endurance running, cycling, lightweight rowing and weight-class combat sports. This calculator scores male athletes on every factor except menstrual function and adjusts the maximum accordingly.

Recovery Is Asymmetric

Restoring intake produces very different timelines across systems. Endocrine markers such as leptin and triiodothyronine respond within days to weeks. Menstrual function typically takes several months to return. Bone mineral density is measured in years, and some loss may never be recovered. That asymmetry is the practical argument for early screening: the cost of investigating a borderline result is small, and the cost of a missed case compounds over a career.

Limits of This Tool

The IOC's RED-S Clinical Assessment Tool is administered by a clinician after full history, examination and laboratory work. This calculator computes energy availability exactly and organises the common risk indicators into a structured, reproducible score. It is a screening aid intended to prompt referral. It cannot diagnose RED-S, an eating disorder, or any other condition. If a result concerns you, or you are worried about your own eating or that of an athlete you coach, seek assessment from a sports physician and an accredited sports dietitian rather than self-managing.