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: metabolism naturally decreases with age (about 1–2% per decade after 20)
• 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 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 merely restful conditions and comes out about 10% higher.

Worth being straight about what this page computes. Mifflin-St Jeor is a BMR equation, fitted against measured basal rates. Nearly every calculator on the web labels its output RMR, and in practice the terms have collapsed into each other. What you get here is a predicted basal rate. If you want a genuine RMR figure, add roughly 10%.

That distinction rarely changes a decision, because both numbers get multiplied by an activity factor whose own error is far larger. It matters when you are comparing this against a metabolic cart measurement from a lab, which will read higher.

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. That is steeper than the 1 to 2% per decade often quoted, because the equation is capturing the loss of lean mass that usually comes with age rather than a change in metabolism per kilogram of tissue. Keep the muscle and the decline is much smaller than the equation assumes.