Cunningham Equation Calculator (RMR for Athletes)
Estimate resting metabolic rate with the Cunningham equation (500 + 22 × lean body mass), the formula preferred for athletes, plus daily calories by activity level.
How it works
Fat-free mass (kg) = weight × (1 − body fat % ÷ 100) · RMR = 500 + 22 × fat-free mass (kcal/day) · daily needs = RMR × activity factor
Cunningham (1980) re-analysed the Harris-Benedict data and showed that lean body mass explained most of the variation in metabolic rate, independent of sex and age. Because muscular athletes burn more at rest than their weight alone predicts, sports dietitians often prefer this equation for trained people. It needs a body-fat estimate — from skinfolds, DXA or bioimpedance — and gives values about 8–10% higher than the similar Katch-McArdle formula (370 + 21.6 × fat-free mass).
Worked example
A 75 kg athlete with 16% body fat: fat-free mass = 75 − 12 = 63 kg; RMR = 500 + 22 × 63 = 1,886 kcal/day. Moderately active (× 1.55): about 2,923 kcal/day. Katch-McArdle gives 1,731 kcal/day.
Sources: Cunningham JJ (1980) A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr 33:2372–2374 · ten Haaf T, Weijs PJM (2014) Resting energy expenditure prediction in recreational athletes. PLoS One 9:e108460
Frequently asked questions
Who should use the Cunningham equation?
It suits athletes and very active people with more muscle than average, because it is based on lean mass. For the general population with no body-fat measurement, Mifflin-St Jeor is usually the better choice.
What is the difference between Cunningham and Katch-McArdle?
Both use fat-free mass. Cunningham is 500 + 22 × FFM, while Katch-McArdle is 370 + 21.6 × FFM, so Cunningham is higher by roughly 150 kcal for a typical athlete. Studies in athletes found Cunningham closer to measured values in many cases.
How accurate does my body fat need to be?
Every 1% of body-fat error changes fat-free mass by about 0.75 kg for a 75 kg person, which moves the result by roughly 16 kcal/day — so the estimate tolerates small measurement errors well.
Is this resting or basal metabolic rate?
Cunningham describes it as resting metabolic rate. In practice the difference from basal metabolic rate is small (a few percent) and both are multiplied by an activity factor to estimate daily needs.
Related calculators
This calculator gives general nutrition estimates and is not medical advice. Energy and nutrient needs vary between people; children, pregnant people and anyone with a medical condition should follow a doctor or registered dietitian.