BMR calculator

The two formulas

BMR is short for basal metabolic rate: the energy you use to stay alive while resting. Labs measure it with indirect calorimetry, which tracks the oxygen you use and the carbon dioxide you breathe out. Nobody does that at home, so apps use equations fitted to people who were measured.

Mifflin-St Jeor (weight in kg, height in cm, age in years)
Men:    10 x weight + 6.25 x height - 5 x age + 5
Women:  10 x weight + 6.25 x height - 5 x age - 161

Katch-McArdle (needs your body fat)
BMR = 370 + 21.6 x lean mass in kg
lean mass = weight x (1 - body fat / 100)

Mifflin and colleagues fitted their equation to 498 healthy adults aged 19 to 78 whose resting energy expenditure was measured by indirect calorimetry. The full version in the paper uses 9.99 where this page uses 10 for weight, and 4.92 where it uses 5 for age. The authors report that the simplified form predicted just as well, and the two differ by under 10 calories a day. Strictly, the equation predicts resting energy expenditure, measured under easier conditions than a true basal test, so "resting burn" is the more accurate name.

Katch-McArdle swaps total weight for lean mass, so it can tell a heavy, muscular person from a heavy person with more body fat. The catch is that it is only as good as the body fat number you give it. A 3.5-point error in body fat, which is normal for a tape-measure estimate, moves the result by about 60 calories for an 80 kg person (2.8 kg of lean mass x 21.6).

A worked example

A 30-year-old man, 180 cm tall, 80 kg, 15% body fat.

• Mifflin-St Jeor: 10 x 80 + 6.25 x 180 - 5 x 30 + 5 = 800 + 1,125 - 150 + 5 = 1,780 calories.
• Lean mass: 80 x (1 - 0.15) = 68 kg. Katch-McArdle: 370 + 21.6 x 68 = 370 + 1,468.8 = 1,839 calories (1,838.8).
• The two are 59 calories apart, about 3%. That is a typical gap, not an error.

How far to trust it

• A systematic review of four common equations found Mifflin-St Jeor the most likely to land within 10% of measured values, and the authors still warned of notable errors for individuals (Frankenfield and colleagues, 2005).
• Resting burn is about two thirds of a day's energy use, and body size and composition leave around 250 calories a day of person-to-person variation unexplained (Hall and colleagues, 2012).
• In 620 healthy Chilean women, only 39.5% (Katch-McArdle) and 33.1% (Mifflin-St Jeor) fell within 10% of a measured value, and both overshot on average (Molina-Luque and colleagues, 2021). That is one population, but it shows an equation that works on average can still be wrong for most individuals.
• The equations were fitted to adults. Outside the 19 to 78 range, treat the result as rougher still.

BMR is not your daily burn

Resting burn is roughly two thirds of what you use in a day. Digesting food adds 5 to 15% of daily energy expenditure (Westerterp, 2004), and movement makes up the rest. To turn BMR into a daily target, use the calorie and macro calculator, or read how many calories you actually burn.

Sources

1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241-247. doi:10.1093/ajcn/51.2.241
2. Molina-Luque R, Carrasco-Marín F, Márquez-Urrizola C, et al. Accuracy of the resting energy expenditure estimation equations for healthy women. Nutrients 2021;13(2):345. doi:10.3390/nu13020345
3. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775-789. doi:10.1016/j.jada.2005.02.005
4. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr 2012;95(4):989-994. doi:10.3945/ajcn.112.036350
5. Westerterp KR. Diet induced thermogenesis. Nutr Metab (Lond) 2004;1:5. doi:10.1186/1743-7075-1-5

Written November 5, 2026, with the sources read that day. An estimate, not medical advice.