How Many Calories Does Your Body Use Doing Nothing? Understanding BMR

November 17, 2025 •

4 min read

Your body never stops burning calories, even when you're completely still, with basic functions accounting for 60% to 75% of your total daily energy expenditure. The answer to how many calories does your body use doing nothing is found in your basal metabolic rate (BMR), a key health metric for understanding your body's energy needs.

Quick Summary

This article explores the concept of your Basal Metabolic Rate (BMR), detailing how your body burns calories at rest, the key factors influencing this process, and how you can estimate your own daily resting energy needs.

Key Points

BMR vs. RMR: Basal Metabolic Rate (BMR) is the energy for vital functions at complete rest, while Resting Metabolic Rate (RMR) includes some daily low-effort activity and is a more practical measure.
Core Body Function Fuel: Your body uses a large portion of its daily calories, 60-75%, to power involuntary functions like breathing, circulation, and cell repair.
Key Influencers: Your resting calorie burn is primarily determined by body composition (muscle mass), age, sex, and genetics.
Boost Your Baseline: Building and maintaining muscle mass through strength training can increase your BMR, as muscle is more metabolically active than fat tissue.
Calculation is Possible: Equations like the Mifflin-St Jeor formula provide a reliable estimate of your BMR using your weight, height, age, and sex.

What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate, or BMR, is the number of calories your body needs to maintain its most basic life-sustaining functions. Think of it as the energy required to simply keep your engine running, even if you were to stay in bed all day without any activity. These involuntary processes include vital activities like:

Breathing and circulation of blood.
Maintaining your body temperature.
Nerve function and brain activity.
Cell production and repair.

BMR is the single largest component of your total daily calorie burn, comprising a significant portion of your total energy expenditure. It is a minimum metabolic rate and is measured under strictly controlled, resting conditions.

The Difference Between BMR and RMR

While often used interchangeably, there is a slight technical difference between BMR and Resting Metabolic Rate (RMR). RMR is the number of calories your body burns while at rest and is a more practical measurement. It accounts for the energy used during low-effort, day-to-day tasks like getting dressed or walking to the bathroom, whereas BMR is a more clinical measurement performed after a period of fasting. For most people, the difference is negligible, and RMR is a more accurate representation of the calories burned 'doing nothing' in a typical day.

Factors That Influence Your Resting Calorie Burn

Your BMR is highly individual and depends on several key factors, which is why calorie calculators are just an estimate. The major influencers include:

Body Composition: Muscle tissue is more metabolically active than fat tissue. A person with more muscle mass will have a higher BMR, as muscle requires more energy to maintain at rest.
Age: As you get older, your BMR tends to decrease. This is partly due to a natural loss of muscle mass that occurs with aging.
Sex: Men generally have a higher BMR than women. This is attributed to men typically having a higher muscle mass and lower body fat percentage.
Weight and Height: Larger and taller individuals have a larger surface area and typically have a higher BMR. The more mass your body has, the more energy it takes to sustain.
Genetics: Some people are born with naturally faster or slower metabolisms due to genetic predisposition.
Hormones: The thyroid gland plays a key role in regulating your metabolism. Conditions like hypothyroidism can significantly decrease BMR.
Sleep: Poor sleep can disrupt hormone levels that regulate metabolism, potentially lowering your resting calorie burn.

How to Calculate Your Resting Calorie Needs

While lab tests can provide a precise measurement, several equations can help you estimate your BMR. The Mifflin-St Jeor equation is widely considered one of the most accurate methods for the general population.

Mifflin-St Jeor Equation:

Men: $(10 × ext{weight in kg}) + (6.25 × ext{height in cm}) - (5 × ext{age}) + 5$
Women: $(10 × ext{weight in kg}) + (6.25 × ext{height in cm}) - (5 × ext{age}) - 161$

Katch-McArdle Formula: This method is more accurate for leaner individuals who know their body fat percentage, as it calculates resting daily energy expenditure (RDEE) based on lean body mass (LBM).

Calculation Formula: RDEE = 370 + (21.6 x LBM in kg)

To see how different methods compare, here is a breakdown:


Calculation Method	Ideal For	Key Variables	Accuracy	Considerations
Mifflin-St Jeor	Most people	Weight, height, age, sex	High (70% accurate estimate)	The most common and reliable equation for general use.
Revised Harris-Benedict	A historical baseline	Weight, height, age, sex	Good, but less accurate than Mifflin-St Jeor	An older formula, superseded by the Mifflin-St Jeor equation.
Katch-McArdle	Leaner individuals	Lean body mass (LBM)	Highly accurate if LBM is known	Requires knowing your body fat percentage, which can be difficult to measure accurately at home.

What Does This Mean for Your Health?

Understanding your BMR is essential for managing your weight and overall health. Knowing your baseline energy needs allows you to set more realistic calorie goals, whether you are aiming for weight loss, maintenance, or gain.

For weight loss: Creating a calorie deficit (consuming fewer calories than your body burns) is key. Your BMR gives you the base number of calories you need to maintain your bodily functions before you even add exercise.
For maintenance: Consuming a calorie intake that matches your total daily energy expenditure (which includes your BMR, physical activity, and thermic effect of food) helps maintain a stable weight.
To boost your BMR: While you can't drastically change your BMR, increasing your muscle mass through strength training can give it a gentle nudge. Muscle tissue burns more calories at rest than fat tissue.

For more detailed information on metabolism and weight loss, consider consulting reliable sources like the Mayo Clinic.

Conclusion

Your body uses a significant number of calories doing nothing, a function of your Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR). This metabolic process fuels your body's essential functions, from breathing to cell repair. While the exact number varies by individual, understanding the factors that influence your BMR—like age, sex, weight, and muscle mass—is a powerful tool for achieving your health and fitness goals. By estimating your BMR with a reliable formula and making informed lifestyle choices, you can effectively manage your energy balance and make smarter decisions for your well-being.

Frequently Asked Questions

The average number of calories burned by an inactive person is typically between 1,200 and 2,400 per day, with the exact number depending on individual factors like age, sex, and body composition.

Yes, you can moderately increase your BMR. The most effective way is by building muscle mass through strength training, as muscle tissue burns more calories at rest than fat tissue does.

Generally, yes. Taller individuals have a larger surface area and typically have more body mass, which requires more energy to sustain at rest, resulting in a higher BMR.

Your BMR naturally decreases with age, primarily due to a gradual loss of muscle mass. This means older adults generally burn fewer calories at rest than younger individuals.

Yes. Knowing your BMR is a critical starting point for weight management, as it helps you set realistic calorie goals. For weight loss, you must consume fewer calories than your body burns.

On average, men have a higher BMR than women. This is largely because men typically have a higher muscle-to-fat ratio, and muscle burns more calories at rest.

Yes, diet can influence your BMR. Severely restricting calories can cause your metabolism to slow down to conserve energy, while consuming sufficient protein can slightly increase your BMR due to the energy required for its digestion.