Screen your energy availability (EA) — a key metric used in sports science to flag risk of Relative Energy Deficiency in Sport (RED-S) in athletes and highly active people.
Don't know your fat-free mass? Find it with our Lean Body Mass Calculator first.
Energy availability (EA) is the amount of dietary energy left over for your body's normal physiological functions — hormone production, bone health, immune function, reproduction — after the energy cost of exercise is subtracted. It's a core concept in sports nutrition used to screen for Relative Energy Deficiency in Sport (RED-S), sometimes still referred to by the older term "Female Athlete Triad."
The formula, developed by exercise physiology researchers, is:
EA = (Energy Intake − Exercise Energy Expenditure) ÷ Fat-Free Mass
The result is expressed in kilocalories per kilogram of fat-free mass per day (kcal/kg FFM/day).
| EA Level | kcal/kg FFM/day | What It Means |
|---|---|---|
| Optimal | 45 or higher | Sufficient energy for training and normal body function |
| Reduced / Subclinical | 30 – 45 | May begin to impair hormone and metabolic function over time |
| Low Energy Availability (LEA) | Below 30 | Associated with RED-S risk: hormonal disruption, poor bone health, impaired performance |
These thresholds come from research on athletic populations (Loucks et al.) and are most relevant for people training consistently at moderate-to-high volume — not the general population.
If your intake supports a healthy TDEE outside of training, start with our TDEE Calculator to understand your baseline needs, then use this tool to check whether your training load is leaving enough energy for recovery and normal function.
Energy availability requires fat-free mass, not total bodyweight.
Calculate Lean Body Mass →45 kcal/kg of fat-free mass per day or higher is generally considered optimal for supporting normal hormonal and metabolic function alongside training.
Relative Energy Deficiency in Sport (RED-S) is a syndrome caused by prolonged low energy availability, affecting hormone regulation, bone density, immune function, cardiovascular health, and athletic performance. It can affect athletes of any sex.
Fat-free mass (muscle, organs, bone) is the metabolically active tissue that actually drives energy needs. Using it instead of total bodyweight gives a more accurate picture of whether energy intake matches the body's real physiological demands.
A result below 30 kcal/kg FFM/day suggests low energy availability. This calculator is a screening tool, not a diagnosis — talk to a sports medicine physician or registered sports dietitian, especially if paired with missed periods, frequent injuries, or fatigue.