BMR Calculator

The Basal Metabolic Rate (BMR) calculator estimates your basal metabolic rate. This term refers to the energy expended at rest in a moderate neutral environment.

The amount of energy required during rest under moderate conditions when the digestive system is at rest is known as the basal metabolic rate (BMR). It’s the same as calculating how much fuel an idling automobile uses while stopped. Only essential organs, such as the heart, lungs, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin, will consume energy in this condition.

Upkeep accounts for up to 70% of total energy (calories) spent by most people daily. Physical activity accounts for 20% of expenditure, whereas food digestion, commonly known as thermogenesis, accounts for 10%.

For accurate BMR measurement, a person’s sympathetic nervous system must be inactive; that is, the person must be fully rested.

Basal metabolism accounts for most of a person’s overall caloric requirements. We can calculate the daily caloric requirement by multiplying the BMR by a factor of 1.2 to 1.9, depending on activity level.

In most cases, we can calculate BMR using formulas based on statistical data. One of the first equations proposed was the Harris-Benedict Equation. It was updated in 1984 to make it more accurate and used until the Mifflin-St. Jeor Equation was developed in 1990.

The Katch-McArdle Formula is unique because it estimates resting daily energy expenditure (RDEE). It considers lean body mass, which the Mifflin-St. Jeor and the Harris-Benedict Equations do not do.

The Mifflin-St. Jeor is the most accurate for determining BMR, except the Katch-McArdle Formula may be more accurate for slimmer persons who know their body fat percentage.

The calculator uses three equations, which are stated below:

The Equation of Mifflin-St. Jeor

The Revised Equation of Harris-Benedict

The Formula of Katch-McArdle

• W - body weight in kg
• H - body height in cm
• A - age
• F - body fat in percentage

Variables Affecting Base Metabolic Rate

Age

The older and leaner a person gets, the lower their BMR or the minimum calorie intake required to keep organs functioning at a certain level.

Genetics

Genetic traits passed down from past generations affect BMR.

Muscle Mass

Aerobic training such as running or cycling does not affect BMR. However, anaerobic exercise, such as weight lifting, increases BMR by building muscle mass and increasing resting energy expenditure. Greater muscle mass corresponds to higher BMR levels needed to maintain the body at a certain level.

Diet

We can increase BMR by eating small meals at frequent intervals. You should also avoid starvation. The smartphone enters power-saving mode when the battery level reaches 5%. Similarly, the human body will sacrifice energy levels, emotions, physical appearance, and mental operations to use the limited caloric energy better. Starvation can lower BMR by as much as 30%.

Pregnancy

Ensuring the survival of a viable fetus raises BMR. This explains why pregnant women consume more than usual. Also, based on hormonal changes, menopause can increase or decrease BMR.

Supplements

To help lose weight, people take certain supplements or medications that increase BMR. One of the most prevalent is caffeine.

Weather

The energy needed to maintain homeostatic body temperature increases BMR in colder conditions. Similarly, excessive exterior heat might elevate BMR when the body uses energy to cool internal organs. For every 1.36 degrees Fahrenheit increase in the body’s internal temperature, BMR increases by around 7%.

Exercise

Aerobic exercise, such as running or cycling, does not affect BMR. But anaerobic exercise, such as weight training, indirectly leads to a higher BMR. The fact is that anaerobic exercise builds muscle mass and thereby increases the body's energy intake at rest. And the higher the percentage of muscle mass in a person's body composition, the higher the BMR.

Gender

On average, due to having a higher muscle mass and lower body fat percentage, men typically have a higher BMR compared to women. The exact difference in BMR varies based on individual body composition, age, and other factors.

Health status

Illnesses or wounds can increase your metabolic rate by about 2 times because the body needs more energy to recover when sick.

Macronutrient intake

Protein increases BMR by 20% to 30%, fat increases BMR by 5%, and carbohydrates increase BMR by 5% to 10%.

BMR Tests

Online BMR tests based on strict equations are not the most reliable way to determine a person’s BMR. It is preferable to seek medical advice or use a calorimetry instrument to determine BMR.

Metabolism and Basal Metabolism

Basal BMR measures our body's energy expenditure when we have just woken up, have not eaten in the past 12 hours, and our body temperature is at a minimum. Basal metabolism shows how much energy the human body uses to perform basic functions.

Metabolism is a complex process that converts food into energy. This is how our body can function. Our energy expenditures are related to four types of metabolism:

1. Resting or basal metabolism. This process maintains total life activity at rest and expends between 50%-75% of total energy.
2. Non-exercise activity thermogenesis (NEAT). It involves simple body movements such as walking, standing, or changing your posture. Even with this activity, the energy expenditure of the body is substantial. And in some cases, they may be equal to intense physical activity.
3. Food thermogenesis or TEF (thermic effect of food). This includes the processing and digestion of food. Food thermogenesis accounts for about 10% of the body's total energy expenditures.
4. Thermogenesis from vigorous exercise or TEE (Thermic effect of exercise). This includes energy expenditure from exercise, which is 5%-15% of the body's total energy expenditure.

Basal metabolic rate or BMR (basal metabolic rate) reflects the minimum amount of energy (calories) expended by the human body to sustain itself at rest. Processes involved in metabolism include:

• blood circulation,
• respiration,
• brain activity,
• protein synthesis,
• cellular repair and other processes.

BMR is the rate at which your body converts calories into energy to support life at rest. This factor also affects weight gain or loss and determines the rate of aging. Maximum calorie burn is in providing your body with basic functions. And these functions make up the basal metabolism.

It's commonly understood that most adults have a BMR that requires them to consume somewhere between 1,200 and 1,500 calories per day for women and 1,500 to 1,800 for men to maintain physiological functions at rest. It's important to note that these figures are just for BMR and do not include additional calories needed for daily activities and exercise.

The Calculation of Basal Metabolic Rate

Knowing data such as sex, weight, age, and height, we can determine a person's BMR with an 80-85% accuracy. To calculate this, we will need a formula and data:

• W - body weight,
• A - age,
• H - height in centimeters.

To get the data, let's take the most popular and accurate formula for BMR calculation to date, the Mifflin-St. Jeor formula. It turned out to be the most accurate of all invented to date. And that is why the Mifflin-St. Jeor formula is most often used in BMR calculators.

• BMR for men = 10W + 6.25H - 5A + 5
• BMR for women = 10W + 6.25H - 5A - 161

Next, we will need to multiply the resulting baseline metabolic index by the physical activity ratio to get the number of calories required for the day. Physical activity is divided into 6 categories:

1. Passive activity (complete absence of physical activity or minimal level - BMR × 1.2).
2. Minimal activity (training 1-3 times weekly - BMR × 1.375).
3. Light activity (training 4-5 times weekly - BMR × 1.46).
4. Moderate activity (daily exercise or vigorous exercise 3-4 times a week - BMR × 1.55).
5. Intense activity (exercising 6-7 times a week - BMR × 1.725).
6. Super-intensive activity (high-intensity work, daily and very intense workouts, or professional sports - BMR × 1.9).

Calculation Example

Let's take Maria as an example. She is 160 centimeters tall, weighs 66 kilograms, is 40 years old, and is lightly active as she works in an office and trains in a gym once or twice a week.

Using the BMR formula for women, we calculate her baseline metabolic rate:

BMR = 10W + 6.25H - 5A - 161 = 10 × 66 + 6.25 × 160 - 5 × 40 - 161 = 1299 kcal

To find her Total Daily Energy Expenditure (TDEE), we multiply her BMR by her activity factor. Assuming light activity, we get:

TDEE = 1299 kcal × 1.375 (activity factor) = 1786 kcal

For weight loss, it's recommended to create a caloric deficit. A safe deficit is generally around 500 kcal per day, which would typically result in losing about 0.5 kg per week.

Maria should therefore aim for a daily caloric intake of:

Daily Caloric Intake = TDEE - Calorie Deficit = 1786 kcal - 500 kcal = 1286 kcal

By consuming around 1286 kcal per day, Maria can aim to lose approximately 0.5 kg per week. Note that these are only estimates, and individual results can vary. It's important for Maria to not consume fewer calories than her BMR and to ensure she's getting adequate nutrition. Regular check-ins and adjustments might be necessary for a healthy and sustainable weight loss journey.

The Rules for Weight Management

When you know your BMR, you understand how many calories you burn during the day while at rest or doing some physical activity. With your BMR, you can learn how many calories you need to take to gain muscle mass, lose weight, or maintain weight. Suppose you know how many calories you are getting and burning. In that case, it will be easier for you to reach an optimal and healthy weight.

If the basal metabolism is high and a person is on a low-calorie diet and still leads at least a relatively active lifestyle, exhaustion, eating disorders, and all kinds of diseases related to metabolic disorders may appear. The body will try with all its might not to give up a single calorie, putting everything into action - first and foremost, to serve vital processes.

A low-calorie diet and skipping meals will not give you the desired result. This approach to weight loss can lead to health problems. The fact is that the body is prohibitively intelligent and programmed to survive. Severe caloric restriction is guaranteed to make the body feel that hunger is coming.

The body will adapt to the limited caloric intake and use less energy to accomplish the same tasks. You will end up with a disturbed metabolism, low stamina, and frequent and rapid fatigue. The worst consequence can be malfunctions of vital systems or the development of chronic diseases.

Maybe the situation is the opposite: a person consumes significantly more calories than required. Then it can lead them not only to obesity but also to more dangerous disorders - thyroid disease or metabolic syndrome.

It is not recommended that women eat less than 1,200 kcal per day and men less than 1,800 kcal per day. Rather than starving yourself, balance your diet without any major hikes.

The easiest way to maintain a healthy weight is to balance your calories consumed and your food intake carefully.

To increase your weight, you must increase your calorie intake. If you want to gain weight slowly and steadily, increase your calorie intake by 300 - 500 kilocalories daily. If you're going to gain weight faster, increase your daily calorie intake by 700 - 1,000 kilocalories.

BMR and RMR

In the literature on metabolism, you may come across a term such as RMR (Resting metabolic rate), which means resting metabolic rate.

Resting metabolic rate is the amount of energy your body needs to function at rest. In addition to the body's basic functions, RMR considers additional daily activities that do not require much effort. Such activities include:

• eating,
• walking for short periods of time,
• using to the bathroom,
• consuming caffeine,
• sweating,
• shivering.

RMR can be measured by equations or by laboratory tests. The lab test will require the subject to get a good night's sleep, restrict food intake, and restrict exercise.

The Similarities between RMR and BMR

BMR and RMR indicate the number of calories your body burns when a person is not exercising. This is often about the same number for each person.

The Differences between BMR and RMR

RMR already considers the minimum activity a person engages in during the day. The BMR does not take such activity into account. But that's why BMR allows you more flexibility in calculating the calories you need.

The BMR is usually slightly lower than the RMR precisely because the BMR doesn't take activity metrics into account. And RMR takes into account the light activity during the day.

BMR allows you to use ratios that indicate the type of physical activity during the day. Having a baseline metabolic rate, you can choose the activity level you do and calculate the amount of calories you need. To do this, you must multiply your BMR by the coefficient corresponding to one of the six physical activity levels.

Modern Knowledge

An average individual consuming a standard diet will have expected BMR numbers. However, some aspects that specifically affect BMR are still not sufficiently explained. Even if scientists control all known metabolic rate factors in studies, that still leaves 26% of the unknown differences between the BMRs of different people.

As a result, even the most exact BMR estimates performed by professionals will not be entirely accurate in their readings. Not all functions of the human body are yet well understood, so the calculation of total daily energy expenditure (TDEE) derived from the BMR estimate is only an estimate.

To achieve any wellness or fitness aim, BMR can help establish the groundwork, but it doesn’t have much to give beyond that.

Keeping a daily log of exercise, food intake, and so on can assist in tracing the aspects that contribute to any given outcome and help you discover what works and what needs improvement.