BMR Calculator

What is Basal Metabolic Rate (BMR)?

Basal metabolic rate (BMR) is the minimum number of calories your body needs to function at rest. This includes the energy your body uses to maintain basic functions such as breathing, circulation, cell production, and nutrient processing.

BMR is influenced by a number of factors, including:

• Age: BMR tends to decrease with age.
• Gender: Men typically have a higher BMR than women.
• Muscle mass: Muscle tissue burns more calories than fat tissue, so people with more muscle mass tend to have a higher BMR.
• Body composition: BMR is calculated based on lean body mass, so people with a higher percentage of lean body mass tend to have a higher BMR.
• Activity level: BMR is also influenced by activity level. People who are more active tend to have a higher BMR than people who are less active.

To calculate your BMR, you can use a number of different formulas. One of the most common formulas is the Mifflin-St Jeor equation.

What is TDEE ?

TDEE stands for Total Daily Energy Expenditure. It's the total number of calories that your body burns in a day when accounting for all activities—everything from digesting food to breathing and walking, to any exercise or physical work you do. TDEE is an important metric for anyone looking to lose weight, gain weight, or maintain their current weight because it provides a calorie target to aim for.

Methods to calculate BMR

1. Mifflin-St Jeor Equation

The Mifflin-St Jeor Equation is considered by many researchers to be one of the most accurate methods for estimating BMR. It was developed in 1990 and is said to be more accurate than the older Harris-Benedict Equation.

Formula:

For men:

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

For women:

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

2. Harris-Benedict Equation

The Harris-Benedict Equation was one of the earliest equations used to estimate BMR. It takes into account weight, height, age, and sex.

Original Formula:

For men:

BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) − (6.75 × age in years)

For women:

BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) − (4.676 × age in years)

3. Revised Harris-Benedict Equation

Due to inaccuracies found in the original Harris-Benedict equation, it was revised in 1984 to better match modern lifestyles.

Revised Formula:

For men:

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

For women:

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

4. Schofield Equation

The Schofield Equation is based on meta-analyses of BMR studies from various countries. It provides different formulas for different age groups.

Formula (This equation has multiple forms depending on age and sex. Here is one example for adults):

For men (18-30 years):

BMR = (0.0630 × weight in kg + 2.8957) × 239

For women (18-30 years):

BMR = (0.0621 × weight in kg + 2.0357) × 239

5. Katch-McArdle Formula

The Katch-McArdle Formula is unique in that it takes into account lean body mass (LBM), making it potentially more accurate for individuals who are highly muscular and those who are significantly leaner than the average population.

Formula:

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

Lean body mass can be calculated using body fat percentage and total weight.

What factors affect BMR?

Several factors can affect Basal Metabolic Rate (BMR), making it higher or lower than the average for people of similar age, sex, weight, and height. Here are some of the primary factors:

1. Age: BMR generally decreases with age due to loss of muscle mass (sarcopenia) and changes in hormonal and neurological processes.
2. Sex: Typically, men have a higher BMR than women because they tend to have more muscle mass and less body fat.
3. Genetics: Metabolic rate can be partly inherited from your parents, influencing your BMR.
4. Body Composition: Muscle tissue requires more energy to maintain than fat tissue. Individuals with more muscle mass have a higher BMR.
5. Weight: Heavier individuals will generally have a higher BMR because they have more mass to support.
6. Height: Taller individuals tend to have a higher BMR as they usually have a larger organ size and surface area.
7. Body Temperature/Health: Fever or illness can raise the BMR as the body works harder to fight off infection. Thyroid function also plays a significant role; hyperthyroidism increases BMR, while hypothyroidism lowers it.
8. Environmental Temperature: Being in a cold environment can increase BMR as the body needs to produce more heat to maintain its internal temperature.
9. Nutritional Status: Starvation or severe calorie restriction can lower BMR as the body becomes more efficient at using energy.
10. Pregnancy and Lactation: BMR increases during pregnancy and lactation due to the energy demands of supporting the fetus and producing milk.
11. Physical Activity: While BMR is a measure of resting metabolic rate, overall daily physical activity can lead to an increase in muscle mass, which in turn can raise BMR.
12. Hormonal Levels: Hormones control metabolism and can affect BMR. For example, an increase in the hormone cortisol can decrease muscle mass and thus BMR.
13. Sleep: Quality and length of sleep can affect metabolic processes and thus influence BMR.
14. Caffeine and Nicotine: These substances can stimulate metabolic rate and may temporarily increase BMR.

Understanding these factors is important because they help explain why two people with similar outward characteristics might have quite different energy needs. Moreover, these factors can vary throughout life, causing fluctuations in BMR over time.