How TDEE is calculated

Step one: the resting equation

Mifflin-St Jeor, published in 1990, gives resting energy expenditure in kcal per day as 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, then plus 5 for men or minus 161 for women. For an 80 kg, 180 cm, 30-year-old man that is 800 + 1,125 - 150 + 5, which is 1,780 kcal. The same body with the female constant gives 1,614. This is the part of TDEE that comes from a paper: a regression fitted to measured resting metabolic rates, with a published derivation you can read.

Step two: the multiplier, which is not from a paper

The ladder of 1.2, 1.375, 1.55, 1.725 and 1.9 that every calculator offers has no primary source. It is a field convention, and this site marks it as one in its formula pack rather than dressing it up. The published counterpart is the FAO/WHO/UNU physical activity level framework, which documents three lifestyle bands for adults: 1.40 to 1.69 sedentary or light, 1.70 to 1.99 active or moderately active, and 2.00 to 2.40 vigorously active. Two rungs of the conventional ladder - 1.2 and 1.375 - sit below the lowest band FAO/WHO/UNU documents at all, which is worth knowing before picking one.

The error to carry with the answer

Frankenfield's 2005 systematic review judged resting-metabolic-rate equations by how often they landed within 10 percent of a measured value. Mifflin-St Jeor did that for more people than any other equation reviewed, which necessarily also means it missed by more than 10 percent for some of them. That is where the band in the table comes from: 1,780 kcal becomes 1,602 to 1,958, and multiplying through by 1.55 turns a tidy 2,759 into 2,483 to 3,035. The multiplier adds error of its own that nobody has quantified, so the true band is wider than the printed one, not narrower.

What the number is not

It is not a measurement. Total daily energy expenditure is measured with doubly labelled water, and resting expenditure with indirect calorimetry; neither is what a web form does. It is also not a per-day truth: expenditure moves with what you did yesterday, how much you slept, how warm the room is and how much you fidget - the last of which has its own name, NEAT. The practical check is not a better equation. It is watching your weight over two or three weeks at a steady intake and adjusting the estimate to what actually happened.

Official sources

• Mifflin, St Jeor et al., A new predictive equation for resting energy expenditure, Am J Clin Nutr 1990
• FAO/WHO/UNU Expert Consultation, Human energy requirements (2004) — physical activity level bands
• Frankenfield, Roth-Yousey & Compher, Comparison of predictive equations for resting metabolic rate, J Am Diet Assoc 2005
• Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005)

Frequently asked questions