Resting Metabolic Rate Calculator

Resting Metabolic Rate (RMR) is the number of calories your body burns at rest to maintain basic life functions like breathing, circulation, and cell repair. It accounts for 60–75% of your total daily energy expenditure.

Mifflin-St Jeor Equation:

For males:
RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5

For females:
RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

What each variable means:

• Weight (kg): more body mass requires more energy to maintain
• Height (cm): taller individuals have a higher surface area and metabolic demand
• Age: the equation takes off 5 calories a year (more on that below)
• Sex: males typically have higher RMR due to greater lean muscle mass

RMR versus BMR, and which one this actually is

BMR (Basal Metabolic Rate) is measured under strict laboratory conditions: after an overnight fast, lying still, in a thermally neutral room, having not exercised for a day. RMR (Resting Metabolic Rate) is measured under looser restful conditions and usually comes out about 10% higher.

Mifflin and St Jeor’s 1990 paper called theirs an equation for resting energy expenditure. They measured 498 healthy adults aged 19 to 78 by indirect calorimetry, in the morning after an overnight fast and lying at rest. Those conditions sit close to basal, which is why the same equation turns up on BMR and RMR calculators alike, including this site’s BMR Calculator. So read the result as a resting rate and do not add another 10% on top.

In a 2005 review for the American Dietetic Association, Frankenfield and colleagues found Mifflin-St Jeor the most accurate of the common equations for healthy adults. Even so, it misses by more than 10% for a sizeable minority of people, and a metabolic cart measurement from a lab is the only way to know which side of it you sit.

When to use this calculator:

• Setting calorie targets for weight loss or gain
• Understanding your baseline energy needs
• Comparing your metabolism before and after lifestyle changes
• Working with a nutritionist or dietitian

Worked example

A 30-year-old male, 178 cm and 80 kg:

(10 × 80) + (6.25 × 178) − (5 × 30) + 5
= 800 + 1,112.5 − 150 + 5
= 1,768 calories a day

That is what he burns existing, before any movement at all. On a sedentary day at ×1.2 it comes to about 2,120.

Daily calorie multipliers (TDEE):

Those multipliers are the weakest part of the whole calculation. The equation itself predicts basal rate within about 10% for most people, but “moderately active” covers an enormous range of actual behavior, and picking one band too high is the most common reason a calorie target does not work. If in doubt, choose the level below the one you think applies and adjust from what the scale actually does over three or four weeks.

Things that genuinely move the number

• Muscle is more metabolically active than fat, so strength training raises resting rate, though by less than fitness marketing suggests: roughly 13 calories a day per kilogram of muscle gained.
• Prolonged aggressive dieting lowers resting rate by more than the weight loss alone accounts for, an effect called adaptive thermogenesis. It is real, and it is one reason very low calorie diets stop working.
• Sleep restriction reduces resting metabolic rate, but modestly. Controlled studies put it around 2 to 5%, not the 20% that gets quoted around the internet.

About the age term

The equation subtracts 5 calories per year, which is about 50 per decade, or roughly 3% of a typical result. Most of that is not metabolism slowing down. Pontzer and colleagues (Science, 2021) measured 6,421 people from infancy to 95 and found that, once body size and lean mass are allowed for, energy use holds steady from about 20 to 60 and only then falls, by about 0.7% a year. The age term is mostly standing in for the muscle people lose as they get older. Keep the muscle and the decline is much smaller than the equation assumes.