Resting Metabolic Rate (RMR) Calculator
Your Resting Metabolic Rate (RMR) is the number of kilocalories your body burns each day while at rest, powering your organs, maintaining body temperature, and keeping your cells functioning. It represents the largest single component of your total daily energy expenditure, typically accounting for 60 to 75 percent of all calories burned each day. Knowing your RMR is a useful starting point for planning calorie intake, whether the goal is weight loss, maintenance, or muscle gain. This calculator uses the revised Harris-Benedict equation published by Roza and Shizgal in 1984, which remains one of the most widely cited predictive equations for RMR. For comparison, it also shows the BMR estimated by the Mifflin-St Jeor equation (1990), which some research suggests is slightly more accurate on average for general populations. Both equations require sex, age, body weight in kilograms, and height in centimetres. Neither equation directly accounts for body composition: two people with identical weight, height, age, and sex can have meaningfully different metabolic rates if one has substantially more muscle mass. These figures are estimates. Individual metabolic rate varies due to genetics, hormonal status, body composition, medications, and health conditions. Consult a registered dietitian or healthcare provider before making significant changes to your diet or calorie intake.
Your RMR (Harris-Benedict revised) is -- kcal/day.
How RMR and BMR are calculated
The revised Harris-Benedict equation (Roza and Shizgal, 1984) corrects the original 1919 Harris-Benedict coefficients using updated regression analysis. The Mifflin-St Jeor equation (1990) was derived from a study of 498 adults and is frequently recommended by dietetic associations as a reasonably accurate population-level estimate.
RMR male (Harris-Benedict revised):
88.362 + (13.397 x weight_kg) + (4.799 x height_cm) - (5.677 x age)
RMR female (Harris-Benedict revised):
447.593 + (9.247 x weight_kg) + (3.098 x height_cm) - (4.330 x age)
BMR male (Mifflin-St Jeor):
(10 x weight_kg) + (6.25 x height_cm) - (5 x age) + 5
BMR female (Mifflin-St Jeor):
(10 x weight_kg) + (6.25 x height_cm) - (5 x age) - 161
Worked example
Male, age 35, weight 75 kg, height 175 cm:
- RMR (H-B revised): 88.362 + (13.397 x 75) + (4.799 x 175) - (5.677 x 35) = 88.362 + 1,004.775 + 839.825 - 198.695 = 1,734.27 kcal/day
- BMR (Mifflin-St Jeor): (10 x 75) + (6.25 x 175) - (5 x 35) + 5 = 750 + 1,093.75 - 175 + 5 = 1,673.75 kcal/day
- Difference: 1,734.27 - 1,673.75 = 60.52 kcal/day
Comparing the two equations
| Equation | Published | Measures | Notes |
|---|---|---|---|
| Harris-Benedict revised (Roza & Shizgal) | 1984 | RMR | Correction of original 1919 H-B; widely used in clinical nutrition |
| Mifflin-St Jeor | 1990 | BMR | Derived from 498 adults; recommended by many dietetic associations for non-obese adults |
Both equations estimate resting energy expenditure from easily measured variables (sex, age, weight, height). Neither accounts directly for body composition. For individuals with high muscle mass or very high body fat, a body-composition-based equation (such as the Katch-McArdle formula using lean body mass) may be more accurate. Indirect calorimetry, performed in a clinical or research setting, is the reference standard for measuring metabolic rate.
Note: these figures are estimates. Body composition, hormonal status, genetics, medication, and health conditions all affect individual metabolic rate. Consult a registered dietitian or healthcare provider before making significant dietary changes.
Using your RMR result
RMR alone does not tell you how many calories to eat each day. To estimate total daily energy expenditure, multiply your RMR by an activity factor (see our TDEE calculator). A commonly used set of activity multipliers ranges from 1.2 (sedentary) to 1.9 (very active). Your calorie target for weight management is then your TDEE adjusted upward or downward depending on your goal.
A deficit of approximately 3,500 to 3,850 kcal is often cited as roughly equivalent to 0.5 kg of body fat. However, this is a simplification: actual weight change depends on the composition of weight lost (fat versus lean mass), metabolic adaptation, and many other factors. A sustainable rate of loss for most people is 0.25 to 0.5 kg per week, achieved through a deficit of roughly 275 to 550 kcal per day.
Resting metabolic rate: frequently asked questions
What is the difference between RMR and BMR?
Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) both estimate the number of calories your body burns at rest, but the measurement conditions differ slightly. BMR is measured under strict clinical conditions: first thing in the morning, after a full night's sleep, in a thermoneutral environment, and after a 12-hour fast. RMR is measured under less stringent conditions, typically just after a period of rest without the overnight fast requirement. In practice, RMR tends to run about 10 to 15 percent higher than BMR for the same individual. For most everyday purposes the two terms are used interchangeably.
Which equation is more accurate: Harris-Benedict revised or Mifflin-St Jeor?
Research has found the Mifflin-St Jeor equation (published 1990) to be slightly more accurate on average for non-obese adults when validated against indirect calorimetry, which is the gold standard for measuring metabolic rate. The revised Harris-Benedict equation (Roza and Shizgal 1984) is also widely used and produces similar results. Neither equation accounts for body composition directly; lean mass strongly influences metabolic rate, so individuals with unusually high or low muscle mass may see larger deviations from predicted values.
How can I use my RMR to manage weight?
Your RMR is the minimum calorie intake needed to sustain basic organ function at rest. Total daily energy expenditure (TDEE) is your RMR multiplied by an activity factor. To lose weight, you consume fewer calories than your TDEE; to gain weight, you consume more. A deficit of around 3,500 to 3,850 kilocalories is commonly cited as approximately equivalent to 0.5 kg (about 1 lb) of fat, though actual results vary. Work with a registered dietitian or healthcare provider to set realistic and safe calorie targets.
Does muscle mass affect RMR?
Yes, significantly. Lean muscle tissue is metabolically active and burns more calories at rest than fat tissue. Individuals with higher muscle mass have higher RMR values than individuals of the same weight with more body fat. This is one reason the prediction equations can be less accurate for athletes or bodybuilders (who may be under-predicted) and for sedentary individuals with high body fat percentages (who may be over-predicted). Resistance training is one of the most effective ways to raise RMR over time.
What factors reduce RMR over time?
RMR tends to decrease with age, partly because muscle mass typically declines after the mid-30s (sarcopenia) and partly due to hormonal changes. Very low calorie diets can also reduce RMR as the body adapts to conserve energy. Thyroid disorders, particularly hypothyroidism, are a common medical cause of reduced metabolic rate. Conversely, hyperthyroidism, fever, and some medications can raise RMR. If you suspect a metabolic condition, consult a healthcare provider for a clinical assessment.
Official sources
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. J Am Diet Assoc. 1990;90(3):452-457.
- U.S. Dietary Guidelines Advisory Committee: Dietary Guidelines for Americans 2020-2025.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information, not medical advice.