What it does
How much energy does a person use in a day? Nutrition and dietetics students learn to estimate it in two steps. First, resting energy expenditure (REE, close to the basal metabolic rate or BMR): the energy used lying still, which is most of the day’s total for most people. Second, the total (sometimes called TDEE): resting energy times an activity factor for everything else.
This calculator works out resting energy with four well-known equations side by side, so you can see how much they differ:
- Mifflin-St Jeor (1990): 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years), then + 5 for men or − 161 for women. Often the first choice for healthy adults today.
- Harris-Benedict (1919): the classic equation from Harris and Benedict’s study of basal metabolism, with their original coefficients.
- Harris-Benedict, Roza-Shizgal (1984): the same form re-fitted to newer data.
- Katch-McArdle: 370 + 21.6 × lean body mass (kg). It ignores sex and age but needs the body fat percentage, from which lean mass = weight × (1 − fat % ÷ 100).
How to use it
- Choose the sex used by the equations, then type age, weight (kg or lb) and height (cm or inches).
- Add body fat % if you know it, for Katch-McArdle. Leave it empty otherwise.
- Pick an example activity level, or type your own activity factor. The examples (1.2, 1.375, 1.55, 1.725 and 1.9) are rounded teaching values and only approximate.
- Read the table: resting energy and the total for each equation. The big line gives the range across the equations. Switch to kJ if your country uses kilojoules (1 kcal = 4.184 kJ).
- Under Weight change, roughly, type a daily energy gap, such as −500 kcal, to see what the simple 7700 kcal per kg rule suggests.
- Download the result as an image, a PDF or a Word file.
Worked example
The page opens with a woman aged 35, 65 kg, 165 cm, 30 % body fat, with the moderate example factor 1.55. Mifflin-St Jeor gives 10 × 65 + 6.25 × 165 − 5 × 35 − 161 = 1,345 kcal at rest and 2,085 kcal in total. Harris-Benedict (1919) gives 1,418 and 2,198, Roza-Shizgal 1,408 and 2,183, and Katch-McArdle (lean mass 45.5 kg) 1,353 and 2,097. So the page shows About 2,085 to 2,198 kcal a day in total. With a gap of −500 kcal a day it suggests eating about 1,585 kcal, roughly 0.45 kg less per week at first.
Weight change: read this
The 7700 kcal per kg rule assumes the body keeps using the same energy as weight falls. It does not: a smaller body uses less, so a fixed gap shrinks over time and the real loss slows down (Hall et al., 2011). Use the number as a rough first-weeks guide only. Eating below the resting energy, very fast loss, and anything for children, pregnancy, older adults or illness needs a qualified professional.
Frequently asked questions
Which equation is right? None exactly. Studies find Mifflin-St Jeor closest for many healthy adults, but any of them can be off by 10 % or more for one person. Measured values (indirect calorimetry) are better when it matters.
Why does it ask for sex? The original studies fitted separate equations for men and women. Katch-McArdle does not use it.
Is anything stored? No. Nothing you type is stored or sent anywhere.
For study and teaching, not medical advice. Check with a qualified professional.
Where the numbers come from
- Mifflin M.D., St Jeor S.T. et al. (1990), A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition 51:241-247.
- Harris J.A., Benedict F.G. (1919), A Biometric Study of Basal Metabolism in Man, Carnegie Institution of Washington, publication 279.
- Roza A.M., Shizgal H.M. (1984), The Harris Benedict equation reevaluated, American Journal of Clinical Nutrition 40:168-182.
- Katch-McArdle: 370 + 21.6 × lean body mass, as given in McArdle, Katch and Katch, Exercise Physiology (textbook).
- Weight change: the 7700 kcal per kg rule of thumb, with the caution from Hall K.D. et al. (2011), The Lancet 378:826-837.
- Activity factors: rounded example values, labelled approximate and editable.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.