The basal metabolic rate (BMR) is the energy the body spends at complete rest: on breathing, circulation, the work of the brain and kidneys, and maintaining body temperature. This is the largest item of daily energy expenditure — it accounts for about 60–70% of all calories.
The basal metabolic rate is the foundation of metabolism and the starting point for calculating daily energy expenditure. It is higher the more lean body mass a person has, so it depends directly on body composition.
How much energy goes to rest
In an adult the basal metabolic rate is usually 1000–2000 kcal a day; in a 2005 Scottish study the values ranged from 1027 to 2499 kcal, with an average of about 1500 kcal. Of total daily energy expenditure, about 70% goes to basal metabolism, another ~20% to physical activity and about 10% to digesting food.
What the basal metabolic rate depends on
The main factor is the amount of metabolically active tissue, that is, lean body mass (muscle and organs). So at the same weight men usually have a higher BMR than women. Thyroid hormones speed up or slow down metabolism, and fever, infections and burns raise it.
With age the basal metabolic rate falls by about 1–2% per decade after 20 — mainly because of the loss of muscle mass. This is exactly why sarcopenia and inactivity lead to fat gain even without overeating.
How it is measured and estimated
The reference method is indirect calorimetry: measuring oxygen consumption and carbon dioxide output at rest, fasting, in a comfortable temperature. In everyday life BMR is estimated from formulas based on sex, age, height and weight — for example, the Harris–Benedict equation or the Mifflin–St Jeor formula.
Why it matters for longevity
The basal metabolic rate links body composition, nutrition and activity. By preserving muscle with strength training and adequate protein, you can maintain a higher basal metabolism with age — this makes weight control and metabolic health easier. Metabolic-age calculators help estimate "how many years" your metabolism is worth.
Calculate using this marker
Calculators where Basal metabolic rate (BMR) is used directly:
Frequently asked questions
Can you "speed up" your basal metabolic rate?
Sharply and lastingly — almost no. The main contribution comes from lean body mass, so the real way to raise BMR is to build and keep muscle through strength training and adequate protein. Caffeine and spicy food give only a small and short-lived effect.
How does basal metabolic rate differ from resting metabolic rate (RMR)?
BMR is measured under strict conditions: fasting, after rest, in a thermoneutral environment. RMR (resting metabolic rate) is a less strict version, it is 5–10% higher and more convenient in practice. In everyday use the terms are often used interchangeably.