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Energy availability calculator

Short answer

Energy availability is the energy left for the rest of your body after training: calories eaten minus exercise calories, divided by your fat-free mass. Eating 2,200 kcal and burning 600 kcal in training at 60 kg and 20% body fat gives 33.3 kcal per kg of fat-free mass. In a landmark study, hormone pulses were disrupted below 30; 45 was the balanced level.

Last reviewed 28 October 20262 published sourcesNot medical advice

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Energy availability calculator

Use a typical day: calories eaten, calories burned in exercise (from your watch, not counting your normal daily burn) and your body fat percentage.

Enter your intake, exercise calories, weight and body fat.

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Daily intake needed for 45 kcal/kg fat-free mass
Exercise calories	40 kg FFM	50 kg FFM	60 kg FFM	70 kg FFM
0 kcal	1,800 kcal	2,250 kcal	2,700 kcal	3,150 kcal
300 kcal	2,100 kcal	2,550 kcal	3,000 kcal	3,450 kcal
600 kcal	2,400 kcal	2,850 kcal	3,300 kcal	3,750 kcal
900 kcal	2,700 kcal	3,150 kcal	3,600 kcal	4,050 kcal

Intake = 45 × fat-free mass + exercise calories, rounded to 10 kcal.

Where the numbers come from

Loucks and Thuma set the energy availability of regularly menstruating women at 45 kcal per kg of lean body mass a day (the balanced condition) and at 10, 20 or 30, using supervised exercise and a controlled diet. Luteinising hormone pulsatility, which drives the menstrual cycle, held steady at 30 but was disrupted below it (Loucks & Thuma, 2003).

The 2023 International Olympic Committee consensus statement describes low energy availability as a spectrum: mild or short-lived dips can be adaptable, while sustained, problematic low energy availability leads to REDs, which clinicians assess from signs, symptoms and risk factors (Mountjoy et al., 2023 (IOC)).

Getting the inputs right

Fat-free mass needs a body fat estimate; get one from the body fat calculator or the skinfold body fat calculator. For your total daily burn rather than just exercise, use the TDEE calculator.

Keep the deficit honest

Reps logs meals by photo, voice or text with a full macro breakdown, so the deficit you plan is the one you actually eat.

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Common questions

How is energy availability calculated?

Energy availability = (energy intake − exercise energy expenditure) ÷ fat-free mass, in kcal per kg of fat-free mass per day. Exercise energy is only what the workout itself burns, not your everyday burn.

What is low energy availability?

In Loucks and Thuma's study of 29 regularly menstruating women, luteinising hormone pulses were unaffected at 30 kcal per kg of lean mass a day but disrupted below it, so 30 is often quoted as a threshold. The 2023 IOC consensus treats low energy availability as a spectrum, from short-lived and harmless to problematic, rather than one cutoff.

What is RED-S?

Relative Energy Deficiency in Sport (REDs) is the IOC's name for the health and performance problems caused by problematic low energy availability, in athletes of any sex. It is assessed by a clinician from symptoms and health markers, not from this number alone.

Sources

Figures on this page were checked against these publications on 28 October 2026.

Loucks AB, Thuma JR. Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. Journal of Clinical Endocrinology & Metabolism. 2003;88(1):297–311. doi.org/10.1210/jc.2002-020369
Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine. 2023;57(17):1073–1097. doi.org/10.1136/bjsports-2023-106994

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