Calorie Calculator

A calorie calculator estimates how many calories you need in a day, according to your height, age, and gender.

When combined with total daily energy expenditure (TDEE) and ideal weight measurements, calorie counting can help you achieve weight loss goal.

About You


How Active Are You?


About You

How Active Are You?


In this article, we explain how a calorie calculator works, its variables, and how it is affected by BMR and activity levels. We then explain how you can use the calorie calculator along with TDEE to lose weight.

What Is A Calorie Calculator?

A calorie is the unit of energy generated from body metabolism. When you eat, the nutrients present in the food are broken down to produce energy, which is counted as calories.

A calorie calculator is an online tool that gives a rough idea of how many calories you need in a day. This is based on your gender, age, current weight and height, and activity levels.

Calorie calculation involves multiplication of your basal metabolic rate (the minimum amount of energy you need at rest to perform vital functions like breathing, circulation, cell formation, etc.), with a physical activity factor (a standard number, specific for each level of physical activity).

Ideal Daily Calorie Intake  = BMR x Physical Activity Factor

In the following sections of the post, we discuss the variables of the calorie calculator, other factors affecting your energy expenditure (factors that are not included when measuring daily caloric needs).

Variables Of Calorie Calculator

The following are the variables of the calorie calculator:


Body composition varies with gender, and therefore, sex is factored in when counting calories.

Lean body mass and fat percentage are different in men and women. Men naturally have more muscle mass. Additionally, they burn fat faster than women. Both these factors increase lean mass (total weight minus weight gained due to fat), which is directly proportional to energy consumption.

In the case of women, body fat is usually more than muscle mass due to slower fat metabolism. Although the breakdown of micronutrients like vitamins and minerals in women is at a higher rate than in men, macros (proteins, carbs, and fats) are the defining factors of weight.

This is why men tend to have slightly higher energy needs than women.

Note that the difference in BMR is primarily due to body composition, and therefore, women with higher activity levels and lean body mass will have high calorie needs.

Activity Level

Activity level is the most important factor of a calorie calculator.

The more you engage in physical exercise and work, the more calories you burn, and hence, the more energy you need to function.

This is why athletes of intense sports have one of the highest energy needs.

The relation between activity level and energy expenditure can also be gauged from the fact that physical exercise builds muscles, which burn more calories than most other tissues of the body.


Age is one of the most crucial factors influencing your daily caloric needs.

As we age, the linear skeleton (height) shrinks because of friction between bones. This friction increases with time due to the loss of cartilage that helps them glide against one another.

Research estimates a loss of almost 1 cm (one-half inch) every decade after 40 years of age. This reduction in height becomes more rapid once you hit 70.

Other than height, body composition also gradually changes with age as you lose muscle mass and gain body fat. Since fat cells utilize less energy than muscles, the decreased lean mass implies low energy consumption.

The low-calorie needs in seniors are also attributed to the natural fatigue that comes with age.

In contrast with the elderly, young individuals have more muscle mass in relation to body fat percentage, are comparatively more active and are fully developed with a good height. Due to this, their body burns more calories in a day.

Note that calorie calculators have an age limit of 15 to 80 because energy needs in infants and children fluctuate at different stages of development. For example, infants aged 9 months to 15 months have an exceptionally fast metabolism and use 50% more calories than adults.

Height and Weight

Weight and height are important when counting calories, especially for weight loss. Understandably, healthy adults who measure more than others in terms of height and weight need more energy to function.

Thus, their daily calorie needs will be high.

Other Factors Affecting Energy Needs

Your required daily calorie intake is dependent on your metabolism, which is influenced by several factors other than the main variables of calorie calculators.

Some of them include the following:


The exact science through which genetics affect your BMR and calorie requirements is unknown.

However, data suggests that inherited variations in genes, which are characteristic of genetic traits in certain races, naturally increase the metabolic efficiency of the digestive system.


Environmental temperature and weather are important deciding factors of metabolic rate and, therefore, decide your energy needs.

Our cells can only perform adequately at an optimal temperature. For this, we have a built-in system that regulates blood pressure and other functions in the body to maintain a stable environment at all times.

When the external temperature is low, the body accelerates metabolism to produce more heat (energy), which is critical to saving the cells from freezing out /dying.

Similarly, when the environment is too hot, the body expands to increase surface area, allowing the internal heat to escape. This increases basal metabolism.


Pregnancy is another thing that influences your calorie intake requirements but is not considered in BMR formulas.

Weight increases in pregnancy, which naturally raises the BMR. Other than that, the body also needs to fulfill the nutrition needs of the fetus. It is generally suggested that, following the first trimester, 300 calories should be added daily to your total calorie intake.

Note that BMR is at an all-time high throughout gestation (pregnancy), but it reduces a little nearing term.


Any medications you are taking can affect your BMR. This is especially true for weight loss supplements that work by boosting metabolism.

Other than medicines, drugs like caffeine, nicotine, and cocaine also increase BMR. According to a study, 100 mg of caffeine can alone raise your BMR by 3% to 4%.


Sleep influences metabolism and is, therefore, critical to weight loss.

It has been estimated that metabolism slows by 15% when you are asleep and is at its lowest when you wake up in the morning.

Therefore, when it comes to weight loss plan, ensuring an adequate amount of sleep (between 7 to 9 hours) is as important as a well-regulated calorie intake.

Mental Health

If you are trying to lose weight, it is essential to know that mental health also plays a significant role in basal metabolic. Various stress hormones are released when you’re unhappy, anxious, or depressed. This chemicals (hormones) can disturb your metabolism.

While the link between anxiety and weight loss is complex, it is an established fact that mood and mental state significantly influence your caloric needs.

Basal Metabolic Rate BMR

BMR, indicates the how many calories you need to survive.

Even when you are completely at rest, you need the energy to perform tasks like breathing, circulation, and organ functions. While metabolism is slowed at rest, food breakdown is an ongoing process because calories are constantly utilized.

The minimum value of calories you consume at rest is referred to as BMR.

BMR is the minimal energy requirement when a person:

  • Is awake but physically inactive.
  • Mentally at rest, i.e., neither excited nor stressed. This is because when you are anxious, cortisol and adrenaline levels rise in the body, which stimulates the breakdown of fat and carbohydrates, creating an energy surge.

Similarly, excitement triggers the release of dopamine and endorphins, which also influences your normal BMR reading.

  • In absolute fasting state for 6 to 12 hours. Since metabolism increases immediately after food intake, being in a fasting state is important to calculate BMR.
  • In a comfortable, neutrally temperate environment of around standard 20C to 25C, as the metabolic rate varies at lower and higher temperatures.

The result generated from your calorie calculator is your BMR in the ideal setup, i.e., well-rested, physically inactive, absolute fasting state in an optimal environment.

When discussing BMR, it is important to mention resting energy expenditure or resting metabolic rate RMR. While the two are often confused, RMR indicates how many calories your body burns when at rest. This is different and understandably higher than the minimum amount of energy you need at rest, i.e., BMR.

BMR Formula For Minimum Calorie Intake

Three equations, namely Mifflin St. Jeor, Katch Mc. Ardle and Harris-Benedict are used to calculate basal metabolic rate BMR.

Of these Mifflin St. Jeor equation is considered the most reliable for counting calories.

Mifflin St. Jeor Equation

Most BMR calculators use this equation:

For Men

BMR = 10 x weight in kg + 6.25 x height in cm – 5 x age + 5

For Women

BMR = 10 x weight in kg + 6.25 x height in cm – 5 x age – 161

Revised Harris Benedict Equation

The Harris Benedict equation was introduced in 1981. Being the first and easy-to-use formula, it was widely used to calculate the BMR for a healthy weight loss plan.

Later, the equation was modified to generate more accurate results.

However, since the Mifflin St. Jeor equation is more precise and accurate, the revised Harris Benedict formula is not in much use now.

For Men

BMR = 13.397 x weight in kg + 4.799 x height in cm – 5.677 x age + 88.362

For Women

BMR = 9.247 x weight in kg + 3.098 x height in cm – 4.33 x age + 447.593

Katch Mc. Ardle Equation

BMR = 370 + 21.6 (1 – body fat percentage) x weight in kg

Katch Mc. Ardle equation is the only formula that factors in body fat percentage. For people having a higher lean mass, Katch Mc. Ardle is often preferred over the Mifflin St. Jeor equation. Mainly, this formula is used for resting metabolic rate or RMR.

When using the equation, you can check your body fat on any online body fat percentage calculator.

Levels Of Physical Activity

Physical activity is of critical importance in nutrition. For use in formulas, dietary guidelines related to weight loss classify daily activity into following levels:

  • Sedentary or little to no exercise
  • Exercise 1 to 3 times a week
  • Exercise 4 to 5 times a week
  • Daily exercise or excessive physical activity 3 to 4 times a week
  • Intense exercise 6 to 7 times a week
  • Daily very intense exercise

In the above classification:

  • Exercise equals 15 to 30 minutes of increased heart rate
  • Intense exercise is 45 to 120 minutes of increased heart activity
  • Very intense exercise is more than 2 hours of elevated heart rate

Activity Factor

An activity factor is a number that comes from several mathematical calculations. While BMR is the minimum energy value, you need extra energy to perform other daily tasks like walking, running, talking, etc.

Therefore, a calorie calculator multiplies your BMR with the activity factor to generate a more realistic and accurate daily calorie requirement.

The activity factor generally ranges from 1.2 to 1.95 (1.7 for moderately active individuals).

How Many Calories Do You Need In A Day?

While counting how many calories you need in a day is useful to set goals for a sustainable weight loss, it has limitations. There are several factors like muscle mass, ethnicity, bone density, etc., that affect metabolic rate but are not considered in calorie counting formulas.

Therefore, to ensure you don’t encounter an energy deficit with low calorie intake, you should also consider TDEE. In addition to that, using a healthy weight calculator is also essential to check your daily calorie requirement.

Total Daily Energy Expenditure TDEE

TDEE indicates how many calories you burn in a day.

Three main factors determine your TDEE:

  • BMR
  • Activity level (low, high, moderately active)
  • Thermic effect of food

Before we get to TDEE calculation, let’s first discuss the thermic effect of food:

Thermic Effect Of Food

The thermic effect of food is the amount of energy used in breaking down the food. This is directly related to the frequency of food intake, as well as the number of good and empty calories in the food.

Bad or empty calories come from processed or packaged food like sugary drinks, cereals, potato chips, etc. These deposit in the body as fat and lead to unhealthy weight gain.

On the other hand, good calories come from natural sources and do not have any negative health effects when used in adequate amounts.

TDEE Calculation

TDEE calculation is mainly similar to calorie calculation, i.e., BMR is calculated, and is then multiplied by an activity factor.

The best quality calculators also factor in the thermal effect of food; however, some online tools don’t consider it due to its insignificant effect.

Healthy Body Weight Calculator

Ideal weight is defined as the healthy weight, associated with minimum incidence of metabolic problems and other health conditions. This is different for each individual, based on gender and height.

Factors determining healthy weight are:

  • Age
  • Sex
  • Height and current weight
  • Body composition
  • Waist circumference
  • Ethnicity
  • Body size (frame)
  • Activity level

Ideal Body Weight or IBW Formulas

Following formulas are used for healthy weight calculation:

Robinson’s Equation

52 kg + [1.9 kg (for men) or 1.7 kg (for women)] per every inch over 5 feet

Miller’s Equation

56.2 kg + [1.41 kg (for men) or 1.36 kg (for women)] per every inch over 5 feet

Devine’s Equation

Height (cm) – [105 (for men) or 108 (for women)]

Hamwi’s Equation

48 kg for the first 5 ft. + 2.7  kg for each additional inch

45.3 kg for the first 5 ft. + 2.2 kg for each additional inch

Body Mass Index (BMI)

Body mass index is the most accurate indicator of healthy weight.

To calculate BMI, you divide your weight (in kg) with height (in meter square). The ratio then corresponds to any one of the four BMI categories.

  • underweight = <18.5
  • healthy = 18.5 to <25
  • overweight = 25 to <30
  • Obese = 30 or higher

Limitations Of the Healthy Body Weight Calculator

Even though a healthy weight calculator is widely used when setting weight loss goals, it is not 100 percent accurate. This is because the formulas are not complete, i.e., they do not factor in a lot of things affecting weight.

These include:

  • Fat
  • Activity level (athletes and people engaged in intense physical activity can be classified as obese or overweight by BMI, even though they have high muscle mass and are healthy in all aspects.
  • Body composition, i.e., does not distinguish between bone density, fat, and muscle mass (lean body mass).
  • Race (BMI and healthy weight calculations are based on data collected from the white population and have certain limitations when dealing with other ethnicities)

Side Effects Of Calorie Deficit

When you are trying to lose weight, especially by a significant amount, starving yourself for long hours, or strictly restricting your calorie intake can be tempting.

However, even if you eat fewer calories than normal, you need to ensure your calories are adequate (calories required for optimal health), or you can otherwise suffer an energy deficit.

This can also lead to eating disorders like anorexia nervosa, which is an extremely dangerous psychiatric disorder that proves fatal in 5% to 10% of patients within ten years.

Therefore, you need to be aware of the side effects of low calorie intake. The main ones are as follows:

  • Headache
  • Dizziness
  • Cramps
  • Excessive hair fall
  • Nutritional deficiencies
  • Cognitive disorders
  • Metabolic disorders
  • Cardiovascular problems
  • Kidney diseases
  • Weakening of eyesight
  • Weak immunity

Most of these complications stem from low levels of macros.

Proteins, carbohydrates, and fat are the main ingredients that comprise a diet, and therefore, they are the main sources of energy.

Each of these is important for different functions in the body. For example, protein is required to build muscle mass and gene synthesis, as well as for the production of enzymes and hormones required for biochemical and homeostatic reactions in the body.

Carbohydrates, on the other hand, are an instant source of energy. Apart from their role in other body tissues, they are mostly required by the brain, as it burns more calories than any other organ of the body. Hence, a carb deficient diet can lead to cognitive decline, memory loss, and even psychosis in extreme cases.

Fats are energy reserves of the body that contribute more calories than the other two macros. They are especially crucial for the absorption of vitamins A, D, E, and K. These vitamins are essential for many body functions, and their deficiency can lead to severe health complications.

Many people eat fewer calories of fats for weight loss. However, this can lead to malabsorption disorders.

Side Effects Of Obesity

Calorie calculation is important to maintain a healthy weight. While being underweight (due to a very low calorie diet) is harmful, having excessive fat accumulation due to high calorie food or from eating plenty of bad calories is also damaging.

Here are the side effects of obesity:

  • Hypertension (high blood pressure)
  • Type 2 diabetes mellitus
  • Heart disease due to atherosclerosis (plaque formation in heart arteries due to fat buildup)
  • Stroke
  • Gallbladder disease (gallstone or cholilitheiasis)
  • Muscle loss
  • Kidney stones

Tips To Lose Weight

If you are considering losing weight, here’s how you can do it without risking health complications due to energy deficit:


IIFYM, or If It Fit Your Macros Diet, is one of the most popular weight loss plans. Unlike other diets that suggest completely eliminating fat or carbs from your diet, IIFYM believes you can eat anything without obsessively restricting calories, and, still lose weight as long as your macros are in moderation.

Here’s how many calories per gram of macronutrient you get after breaking them down:

  • 1 gm Proteins – 4 calories
  • 1 gm Carbohydrates – 4 calories
  • 1 gm Fats – 9 calories

Ideally, here’s how the macros distribution should be in your diet:

  • Proteins – 10% to 35%
  • Carbohydrates – 45% to 65%
  • Fats – 20% to 35%

When making a meal plan according to your calorie calculator, make sure the food includes all three macros in an ideal proportion.

General Tips

Other than following the IIFYM diet, here are some general tips for more nutrients and healthy weight loss:

  • Minimize alcohol intake for a sustainable weight loss
  • Avoid smoking, as some data suggests strong correlation between heavy smoking and unhealthy, rapid weight loss
  • Avoid processed foods
  • Exercise daily (if the aim is to drop a significant number of pounds, to see how much exercise you need), and stay at least moderately active, even in old age.
  • To avoid calorie deficit and unhealthy weight gain, ensure your weight loss plan includes nutrient dense foods. This is possible by eating plenty of whole grains, meat, eggs, fruits, vegetables, and other sources of high protein diet.
  • Consult a dietician and adhere to their suggested dietary guidelines for weight loss.