BMR Calculator: How Many Calories Does Your Body Burn at Rest?

You burn calories all day, even when you're doing absolutely nothing.

Your heart is pumping blood, your brain is consuming energy, your lungs are moving air, and your body is constantly maintaining thousands of physiological processes that keep you alive.

All of that requires energy.

In fact, for most people, simply maintaining these basic functions accounts for the largest portion of their daily calorie expenditure.

This is known as your basal metabolic rate, or BMR.

Knowing your BMR can be useful if you're trying to lose body fat, gain muscle, maintain your weight, or simply understand how your metabolism works.

But there's an important distinction that gets overlooked quite often.

Your BMR is not the number of calories you should necessarily eat each day.

It's an estimate of the energy your body requires under very specific resting conditions.

To make things easier, we created a free BMR Calculator that estimates your resting calorie requirements using several established equations and shows how those numbers compare with your total daily energy needs.

TLDR

• Basal metabolic rate (BMR) is the energy your body requires to maintain essential physiological functions under standardized resting conditions.
• For many adults, resting metabolism accounts for approximately 60% to 75% of total daily energy expenditure, although this varies with activity level and other factors.
• BMR is influenced by body size, fat-free mass, age, sex, and other physiological characteristics.
• The Mifflin-St Jeor equation is a commonly used method for estimating resting energy expenditure.
• BMR and TDEE are not the same thing. TDEE includes resting metabolism, physical activity, and the energy required to process food.
• Eating exactly your BMR isn't a universal weight-loss strategy and may provide insufficient energy for your needs.
• Online BMR calculators provide estimates. They do not directly measure your metabolism.

Want to calculate yours? Try our free BMR Calculator to estimate your resting calorie expenditure and daily maintenance calories.

What Is Basal Metabolic Rate (BMR)?

Basal metabolic rate is the amount of energy your body uses to maintain essential functions while at complete rest.

These functions include:

• Breathing
• Blood circulation
• Brain and nervous system activity
• Maintaining body temperature
• Cellular repair and maintenance
• Protein synthesis and other metabolic processes
• Normal organ function

Technically, BMR is measured under tightly controlled conditions.

A person must be awake, completely at rest, in a thermally neutral environment, and typically measured after an overnight fast.

Those conditions matter because movement, digestion, temperature, and other factors influence energy expenditure.

In everyday conversation, people often use BMR and resting metabolic rate (RMR) interchangeably.

They're closely related, but they aren't exactly the same measurement.

We'll get into that distinction shortly.

How Many Calories Does Your Body Burn at Rest?

There's no single number that applies to everyone.

A smaller, older adult may have a substantially lower BMR than a larger, younger adult with more muscle mass.

For example, consider two hypothetical individuals.

Person A:

• 35-year-old male
• 180 pounds
• 5 feet 10 inches

Using the Mifflin-St Jeor equation, his estimated resting energy expenditure is approximately 1,750 calories per day.

Person B:

• 35-year-old female
• 140 pounds
• 5 feet 5 inches

Her estimated resting energy expenditure is approximately 1,330 calories per day.

Neither number tells us how many calories these individuals actually burn throughout a normal day.

It only estimates the energy required to support their basic physiological functions at rest.

Once you include walking, working, exercising, and digesting food, total calorie expenditure increases.

That's where TDEE becomes useful.

How to Calculate Your BMR

Several equations have been developed to estimate resting energy expenditure.

Most use some combination of age, height, weight, and sex.

Some also incorporate body composition.

Our BMR Calculator compares three commonly used equations.

1. Mifflin-St Jeor Equation

The Mifflin-St Jeor equation was published in 1990 and remains one of the most widely used equations for estimating resting energy expenditure.

For men:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

For women:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Let's use a 35-year-old male who weighs 180 pounds and is 5 feet 10 inches tall.

First, convert the measurements:

Weight: 81.6 kilograms

Height: 177.8 centimeters

Now enter those values into the equation:

BMR = (10 × 81.6) + (6.25 × 177.8) − (5 × 35) + 5

BMR = 816 + 1,111.25 − 175 + 5

Estimated BMR = 1,757 calories per day

That means the equation predicts approximately 1,757 calories of resting energy expenditure per day.

The important word is predicts.

Your actual energy expenditure could be higher or lower.

2. Harris-Benedict Equation

The original Harris-Benedict equation was developed in 1919.

It was later revised by Roza and Shizgal in 1984.

The revised equation uses weight, height, age, and sex to estimate resting energy expenditure.

For men:

BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)

For women:

BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)

The Harris-Benedict and Mifflin-St Jeor equations often produce slightly different results.

That's expected.

They were developed using different datasets and statistical models.

Neither equation directly measures your metabolism.

3. Katch-McArdle Equation

The Katch-McArdle equation takes a different approach.

Instead of relying on age, height, weight, and sex, it estimates resting energy expenditure using fat-free mass.

BMR = 370 + (21.6 × lean body mass in kg)

To calculate lean body mass:

Lean body mass = Body weight × (1 − Body fat percentage ÷ 100)

For example, suppose someone weighs 180 pounds and has an estimated body fat percentage of 20%.

Their lean body mass would be:

180 × 0.80 = 144 pounds

That's approximately 65.3 kilograms.

Using the Katch-McArdle equation:

BMR = 370 + (21.6 × 65.3)

Estimated BMR = 1,780 calories per day

This approach can be useful when you have a reasonably accurate estimate of body composition.

However, there's a catch.

If your body fat percentage estimate is inaccurate, your calculated BMR will also be affected.

That matters because common body composition methods, including consumer bioelectrical impedance scales, can have meaningful individual measurement errors.

Which BMR Formula Is Most Accurate?

For general use, I would start with Mifflin-St Jeor.

A frequently cited systematic review by Frankenfield and colleagues found that the Mifflin-St Jeor equation performed relatively well compared with several other commonly used predictive equations.

But that doesn't mean it's the most accurate equation for every individual.

People with unusually high or low amounts of muscle mass, certain medical conditions, or other characteristics may differ substantially from the populations used to develop these equations.

Katch-McArdle may be worth comparing if you have reliable body composition data.

And if you need a more precise assessment of resting energy expenditure, indirect calorimetry is generally a better approach than relying solely on prediction equations.

For most people trying to manage body weight, though, a reasonable estimate is sufficient to get started.

BMR vs. TDEE: What's the Difference?

This is probably the most important distinction to understand.

Your BMR represents resting energy expenditure.

Your total daily energy expenditure (TDEE) represents the energy your body uses throughout an entire day.

TDEE includes several components.

Resting Energy Expenditure

This is the energy required to maintain basic physiological functions.

It's generally the largest component of daily calorie expenditure.

Exercise Activity

This includes structured exercise such as running, lifting weights, cycling, swimming, and other training.

The amount varies considerably depending on exercise intensity, duration, and frequency.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT refers to energy expended during activities that aren't structured exercise.

Walking around your home, doing yard work, standing, cleaning, and general movement all contribute.

NEAT can differ substantially between individuals.

Thermic Effect of Food (TEF)

Digesting, absorbing, and processing food requires energy.

The thermic effect of food typically represents a smaller but meaningful portion of daily energy expenditure.

Protein generally has a higher thermic effect than carbohydrates or fat.

Example: BMR vs. TDEE

Let's say your estimated BMR is 1,750 calories per day.

Your total daily energy expenditure might look something like this:

These estimates use commonly applied activity multipliers.

They're convenient, but they're not exact measurements.

Two people who both describe themselves as moderately active may have very different energy expenditures.

For a more detailed estimate, use our Health and Fitness Calculator Hub to access the TDEE Calculator.

What Factors Affect Your BMR?

Several factors influence how much energy your body uses at rest.

Some are modifiable.

Others aren't.

Body Size

Larger bodies generally require more energy to maintain.

This is one reason a 250-pound person will often have a higher resting energy expenditure than a 130-pound person.

Muscle Mass and Fat-Free Mass

Fat-free mass is an important predictor of resting energy expenditure.

Muscle tissue requires energy even when you're not exercising.

However, the idea that gaining a few pounds of muscle will dramatically increase your metabolism is exaggerated.

Skeletal muscle does consume energy at rest, but individual organs such as the brain, liver, heart, and kidneys have much higher metabolic rates per kilogram of tissue.

Building muscle is valuable for many reasons.

A massive increase in resting calorie expenditure usually isn't one of them.

Age

Resting energy expenditure often decreases with age.

Some of that change is associated with reductions in fat-free mass and changes in body composition.

However, age-related metabolic changes are more complicated than the common claim that your metabolism suddenly slows down when you turn 30.

A large study published in Science in 2021 found that energy expenditure adjusted for fat-free mass was relatively stable through much of adulthood before declining later in life.

Sex

On average, men have higher absolute resting energy expenditures than women.

Much of this difference is related to body size and body composition.

Standard prediction equations include sex-specific coefficients, but they cannot capture every individual's physiology.

Genetics

Genetic factors contribute to individual variation in resting energy expenditure.

Even after accounting for body size and composition, people can have somewhat different metabolic requirements.

Energy Restriction and Weight Loss

When you lose weight, your resting energy expenditure generally decreases.

Part of that is expected because there's less body tissue to maintain.

There can also be additional physiological adaptations associated with sustained energy restriction and weight loss.

This is one reason your calorie requirements may change as you lose weight.

Does Your Metabolism Slow Down as You Get Older?

Yes, but probably not in the way most people think.

It's common to hear that metabolism starts declining rapidly after age 30.

The evidence doesn't support such a simple explanation.

In a large analysis involving thousands of participants across the human lifespan, Pontzer and colleagues found that adjusted energy expenditure remained relatively stable from approximately age 20 through age 60.

After that, adjusted energy expenditure declined gradually.

This doesn't mean people can't gain weight during their 30s, 40s, or 50s.

Changes in physical activity, body composition, food intake, and lifestyle can all affect energy balance.

But blaming every pound gained after age 30 on a rapidly slowing metabolism isn't particularly accurate.

Does Having More Muscle Increase Your BMR?

Yes, although the effect is often overstated.

Skeletal muscle is metabolically active tissue.

According to estimates reported in the scientific literature, resting skeletal muscle uses approximately 13 calories per kilogram per day.

That's roughly six calories per pound of muscle per day.

So gaining five pounds of muscle might increase resting energy expenditure by approximately 30 calories per day from the muscle tissue itself.

That's useful, but it isn't the hundreds of extra calories per day that some fitness articles claim.

Of course, building muscle can improve strength, physical function, and body composition.

And the training required to build and maintain that muscle also contributes to overall energy expenditure.

I just wouldn't recommend strength training primarily because you think adding a few pounds of muscle will turn your metabolism into a calorie-burning furnace.

Should You Eat Your BMR Calories to Lose Weight?

Not necessarily.

This is one of the biggest misconceptions surrounding BMR calculators.

If your BMR is 1,700 calories, that doesn't mean you should automatically eat 1,700 calories to lose weight.

Your actual maintenance calories may be considerably higher.

For example:

Estimated BMR: 1,700 calories

Estimated TDEE: 2,600 calories

If you consume 1,700 calories per day, you're creating an estimated 900-calorie deficit.

That may be unnecessarily aggressive, particularly if you're physically active.

A more moderate deficit might be appropriate.

For many adults, starting with a deficit of approximately 300 to 500 calories per day is reasonable, although individual circumstances matter.

The point is that your calorie deficit should generally be calculated from your total daily energy expenditure, not your BMR alone.

Our Calorie Deficit Calculator can help estimate an appropriate starting target.

Can You Increase Your BMR?

You can influence some of the factors associated with resting energy expenditure, but there's no reliable trick that dramatically increases your BMR.

Building or maintaining muscle can modestly increase resting energy requirements.

Changes in body weight and composition can also affect BMR.

But claims that certain foods, supplements, or meal schedules substantially boost resting metabolism are often exaggerated.

Caffeine, for example, can temporarily increase energy expenditure.

However, the effect is generally modest, varies between individuals, and may diminish with habitual use.

It's not a substitute for managing total energy balance.

Why Your Actual Calorie Needs Might Be Different From Your BMR Calculator Results

Prediction equations are based on averages.

Your physiology isn't necessarily average.

Someone with the same age, height, weight, and sex as you could have a different resting metabolic rate.

Differences in fat-free mass, organ size, hormonal status, and other factors contribute to variation.

Activity estimates introduce another source of uncertainty.

The difference between being lightly active and moderately active isn't always obvious.

And an activity multiplier can't perfectly account for the energy cost of every workout or movement throughout the day.

This is why I recommend using BMR and TDEE calculators as starting points.

If your estimated maintenance intake is 2,500 calories but your weight consistently increases while eating that amount, your actual maintenance requirement may be lower.

If your weight consistently decreases, it may be higher.

Your real-world results help refine the estimate.

BMR and Endurance Athletes

If you're an endurance athlete, understanding the difference between BMR and total energy expenditure is especially important.

A runner training for a marathon or ultramarathon may burn a substantial amount of energy through exercise.

But their BMR calculation doesn't directly account for that training.

For example, two athletes could have nearly identical BMR values while having dramatically different total daily energy requirements.

One might run 15 miles per week.

The other might run 70.

Their resting energy needs may be similar, but their total calorie requirements are unlikely to be.

Consistently underestimating energy requirements can increase the risk of low energy availability.

In athletes, prolonged low energy availability can contribute to Relative Energy Deficiency in Sport (REDs), which can affect recovery, hormonal function, bone health, and performance.

If you're training heavily, I would be cautious about using BMR alone to determine calorie intake.

How Often Should You Recalculate Your BMR?

You don't need to recalculate your BMR every week.

However, it can be useful to update your estimate when your body weight or body composition changes substantially.

For example, if you lose 25 pounds, your estimated resting energy expenditure will generally be lower than it was at your starting weight.

That doesn't mean your metabolism is damaged.

It means your body has changed.

You may also want to reassess your total daily energy expenditure when your activity level changes.

Moving from a sedentary routine to training five days per week can substantially change your maintenance calorie requirements, even if your BMR changes very little.

Use Our Free BMR Calculator

We created our free BMR Calculator to help you better understand your resting energy needs.

Enter your age, sex, height, weight, and activity level.

If you know your approximate body fat percentage, you can enter that too.

The calculator will estimate:

• Your basal metabolic rate using Mifflin-St Jeor
• Your resting energy expenditure using the revised Harris-Benedict equation
• Your Katch-McArdle estimate when body fat percentage is provided
• Your estimated total daily energy expenditure
• Maintenance calorie estimates across different activity levels
• The difference between resting energy requirements and total daily calorie expenditure

It's a useful starting point whether you're trying to lose body fat, gain muscle, maintain your weight, or simply understand how your body uses energy.

Frequently Asked Questions

What is a normal BMR?

There is no single normal BMR. Resting energy expenditure varies with body size, fat-free mass, age, sex, and other factors. Comparing your estimated BMR to a population average is usually less useful than understanding your own energy requirements.

How do I calculate my BMR?

One commonly used method is the Mifflin-St Jeor equation, which uses weight, height, age, and sex to estimate resting energy expenditure. You can also use our free BMR Calculator to perform the calculation automatically.

What is the difference between BMR and TDEE?

BMR estimates the energy your body uses at rest. TDEE estimates your total daily energy expenditure, including resting metabolism, physical activity, and digestion.

Is BMR the same as resting metabolic rate?

Not exactly. BMR is measured under stricter laboratory conditions, while resting metabolic rate is typically measured under less restrictive conditions. In everyday nutrition discussions, the terms are often used interchangeably.

Is a higher BMR better?

Not necessarily. A higher BMR often reflects a larger body size or greater fat-free mass. It doesn't automatically indicate better metabolic health.

Does muscle increase BMR?

Yes. Muscle is metabolically active tissue, but the increase in resting calorie expenditure from adding a few pounds of muscle is generally modest.

Does BMR decrease with age?

Resting energy expenditure can decrease with age, partly because of changes in body size and composition. Research suggests that adjusted energy expenditure remains relatively stable through much of adulthood before declining later in life.

Should I eat below my BMR to lose weight?

You do not need to eat below your BMR to lose weight. Weight loss depends on creating a calorie deficit relative to your total daily energy expenditure. Eating below BMR may create an unnecessarily large deficit for some people.

Can a BMR calculator tell me exactly how many calories I burn?

No. Online calculators estimate resting energy expenditure using prediction equations. Direct measurement using indirect calorimetry provides a more individualized assessment.

Which BMR equation is most accurate?

Mifflin-St Jeor is a reasonable starting choice for many adults. However, no equation is universally accurate for everyone, and predictions can differ from measured resting energy expenditure.

References

1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241–247. https://doi.org/10.1093/ajcn/51.2.241
2. Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition. 1984;40(1):168–182. https://doi.org/10.1093/ajcn/40.1.168
3. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775–789. https://doi.org/10.1016/j.jada.2005.02.005
4. Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021;373(6556):808–812. https://doi.org/10.1126/science.abe5017
5. Wang Z, Heshka S, Gallagher D, Boozer CN, Kotler DP, Heymsfield SB. Resting energy expenditure-fat-free mass relationship: new insights provided by body composition modeling. American Journal of Physiology-Endocrinology and Metabolism. 2000;279(3)–E545. https://doi.org/10.1152/ajpendo.2000.279.3.E539
6. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826–837. https://doi.org/10.1016/S0140-6736(11)60812-X
7. Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine. 2023;57:1073–1097. https://doi.org/10.1136/bjsports-2023-106994

About the Author

Matt Mosman, MS, CISSN, CSCS, is the Founder and Chief Science Officer of Simply Good Supplements. With a background in exercise science, sports nutrition, and strength and conditioning, Matt focuses on translating scientific research into practical strategies for improving health, fitness, and athletic performance.