RMR Calculator Guide: Resting Metabolic Rate Explained (2026)
Quick Answer
- *RMR is the number of calories your body burns at complete rest — typically 60–75% of your total daily calories.
- *The Mifflin-St Jeor equation is the most accurate prediction formula for healthy adults.
- *Average RMR: 1,200–1,500 cal/day for women, 1,500–1,800 cal/day for men.
- *Building lean muscle is the most effective way to increase your resting metabolism.
What Is Resting Metabolic Rate?
Resting metabolic rate (RMR) is the total number of calories your body burns while at complete rest to maintain basic life functions: breathing, circulating blood, regulating body temperature, building and repairing cells, and running your brain. For most people, RMR accounts for the largest share of daily calorie expenditure — roughly 60–75%.
The remaining calories come from the thermic effect of food (about 10% of intake) and physical activity (15–30%, depending on how active you are). Understanding your RMR gives you a baseline for planning calorie intake, whether the goal is weight loss, maintenance, or muscle gain.
RMR vs. BMR: What's the Difference?
Basal metabolic rate (BMR) and resting metabolic rate (RMR) are often used interchangeably, but they're technically different. BMR is measured under extremely strict laboratory conditions — after 8 hours of sleep, 12 hours of fasting, in a thermoneutral environment. RMR is measured under less restrictive resting conditions and is typically 10–20% higher than BMR.
For practical purposes, the difference doesn't matter much. The Mifflin-St Jeor equation, the most commonly used prediction formula, technically estimates RMR.
The Mifflin-St Jeor Equation
Validated in a 2005 review by the American Dietetic Association as the most accurate RMR prediction equation for healthy adults:
- Men: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Worked Example
A 35-year-old man, 5'10" (177.8 cm), 180 lbs (81.6 kg):
- RMR = (10 × 81.6) + (6.25 × 177.8) − (5 × 35) + 5
- RMR = 816 + 1,111.25 − 175 + 5 = 1,757 calories/day
What Burns Those Resting Calories?
Your body allocates RMR calories roughly as follows:
| Organ/System | % of RMR | Calories/day (est.) |
|---|---|---|
| Brain | 20% | ~340 |
| Liver | 20% | ~340 |
| Skeletal muscle (at rest) | 20–25% | ~400 |
| Heart | 10% | ~170 |
| Kidneys | 8% | ~136 |
| Other (lungs, GI, etc.) | 17–22% | ~300 |
Factors That Affect RMR
Body Composition
Lean mass (muscle, organs, bone) is far more metabolically active than fat tissue. Each pound of muscle burns about 6 calories per day at rest; each pound of fat burns about 2. This is why two people of the same weight can have very different RMR values.
Age
A 2021 study in Science upended conventional wisdom by showing that metabolism stays remarkably stable from age 20 to 60 when adjusted for body composition. The perceived metabolic slowdown is primarily driven by muscle loss and reduced activity — not an inherent metabolic change. After 60, metabolism does decline about 0.7% per year.
Thyroid Function
Thyroid hormones (T3 and T4) are the primary regulators of metabolic rate. Hypothyroidism can decrease RMR by 10–15%, while hyperthyroidism can increase it by a similar amount. If your measured RMR is significantly different from predicted, thyroid testing is warranted.
Adaptive Thermogenesis
During prolonged calorie restriction, the body can reduce RMR beyond what's explained by weight loss alone — a phenomenon called adaptive thermogenesis or “metabolic adaptation.” Research from the Biggest Loser study (2016) showed participants' RMR dropped 500+ calories below predicted values after extreme dieting. Moderate deficits (300–500 cal/day) minimize this effect.
Calculate your resting metabolic rate
Try the Free RMR Calculator →Frequently Asked Questions
What is the difference between RMR and BMR?
BMR is measured under strict conditions — after 8 hours of sleep, 12 hours of fasting, in a thermoneutral environment. RMR is measured under less restrictive resting conditions and is typically 10–20% higher. In practice, the terms are often used interchangeably.
How is RMR calculated?
The most accurate prediction equation is Mifflin-St Jeor: For men, RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women, subtract 161 instead of adding 5.
Can you increase your resting metabolic rate?
Yes. Building lean muscle mass is the most effective way. Each pound of muscle burns roughly 6 calories per day at rest versus 2 for fat. Strength training 2–3 times per week can increase RMR by 20–30 calories/day over 8–12 weeks. High-protein diets also temporarily boost metabolism through the thermic effect of food.
Does metabolism slow down with age?
A 2021 Science study found metabolism stays stable from age 20 to 60 when adjusted for body composition. The perceived slowdown is primarily due to muscle loss and decreased activity. After age 60, metabolism declines about 0.7% per year.
How many calories does your body burn at rest?
RMR accounts for 60–75% of total daily energy expenditure. A typical adult woman burns 1,200–1,500 calories at rest; a typical adult man burns 1,500–1,800. This energy maintains core body temperature, brain function, organ function, cellular repair, and breathing.