Basal metabolic rate calculator

Several BMR formulas exist, but the most widely used is the Black et al. equation, which takes into account age, sex, height and weight.

Here are the Black et al. formulas (used in this calculator):

Gender	Formula
Men	Kcal = [0.963 x Weight(kg)0.48 x Height(m)0.50 x Age(yr)-0.13] x (1000/4.1855)
Woman	Kcal = [1.083 x Weight(kg)0.48 x Height(m)0.50 x Age(yr)-0.13] x (1000/4.1855)

Other methods do exist, however, and can be compared with our second calculator below:

What is basal metabolic rate?

Basal Metabolic Rate (BMR) represents the minimum amount of energy your body consumes at rest to maintain its vital functions.

It's the energy needed to keep your organs running, maintain body temperature, ensure blood circulation, respiration and all the cellular processes essential to life.

Why is it important to know?

Knowing your basal metabolic rate is essential for :

• Calculate your daily calorie needs according to your activity level
• Plan weight loss by creating an appropriate caloric deficit
• Optimize your sports nutrition to maintain or build muscle mass
• Avoid overly restrictive diets that can slow metabolism

The remainder is divided between :

• Thermic Effect of Food (TEF): ~10%.
• Physical activity (exercise + NEAT): 15 to 30% (but much more in athletes).

How can you change your basal metabolic rate?

Non-modifiable factors

• Age: metabolism declines by around 2-3% per decade after the age of 30, mainly due to loss of muscle mass. However, this phenomenon can be mitigated by an active lifestyle, notably through muscle-strengthening exercises and a suitable diet.
  
• Gender: men generally have a 10-15% higher basal metabolic rate than women, due to higher muscle mass and lower body fat.
  
• Genetics: some people are born with a naturally faster or slower metabolism.
  
• Height and body weight: the taller and heavier you are, the higher your basal metabolic rate.

Modifiable factors

• Body composition: muscle mass burns more calories at rest than fat mass. Elia (1992) and subsequent validation studies show that 1 kg of skeletal muscle burns 13 kcal/kg/day and adipose tissue 4.5 kcal/kg/day at rest.
  
• Physical activity: exercise, particularly weight training, increases metabolism during and after exercise (EPOC effect - Excess Post-Exercise Oxygen Consumption).
  
• Food: the thermal effect of food accounts for 8-10% of total metabolism. Proteins have the highest thermal effect (20-30% of their caloric value).
  
• Sleep: lack of sleep can reduce metabolism by 5-20% and disrupt the hormones that regulate appetite.
  
• Stress: chronic stress can affect thyroid hormones and slow metabolism.
  
• Body temperature: a rise of 1°C can increase metabolism by 10-13%. Metabolism accelerates to meet increased energy requirements, notably to maintain homeostasis or support physiological processes intensified by heat (such as during a fever). This estimate is based on physiological studies, such as the van't Hoff rule, which indicates that metabolic reactions accelerate with temperature.

What impact does basal metabolic rate have on weight loss?

Weight loss follows the principle of energy balance:

• Déficit calorique = Calories consommées < Calories dépensées
• 1 kg fat ≈ 7700 kcal

Too high a deficit (over 25%) in basal metabolic rate can lead to :

• Metabolic adaptation (slower BMR)
• Loss of muscle mass
• Nutritional deficiencies
• A yo-yo effect when you stop dieting

To avoid the yo-yo effect, or simply to preserve health, athletes should aim for a loss of 0.5 to 1% of body weight per week (i.e. a daily deficit of 300 to 500 kcal).

Metabolic pauses" must also be incorporated. This means incorporating caloric maintenance phases every 6 to 12 weeks to "kick-start" the metabolism.

Comparison of calculation methods

Comparison of the main formulas

Formula	Year	Study population	Age limits	Weight limits	Precision	Recommended use
Harris-Benedict	1919	136 men, 103 women, 94 children	21-70 years	25-125 kg	±14% (general population)	Population corresponding to original criteria
Roza-Shizgal	1984	Larger samples than H&B	Adults	Normal weight	±14% (improved)	Healthy general population
Black et al.	1996	Large, diversified samples	>60 years (optimal)	Overweight accepted	High for specific populations	Elderly and overweight people
Mifflin-St Jeor	1990	Diverse modern population	Adults	Broad spectrum	Considered the precise	Modern general population

The Harris-Benedict formula, published in 1919, represents a major historical milestone, being the first to propose a rigorous scientific estimate of basal metabolic rate. Developed from observations on 333 subjects, this formula served as a reference for over six decades, despite significant limitations related to the study population of the time.

The 1980s marked a turning point with the revision by Roza and Shizgal who, aware of demographic and nutritional changes, set about modernizing the Harris-Benedict approach.

Their work has made it possible to improve the accuracy of the estimates by integrating data more representative of contemporary populations, while retaining the simplicity of use of the original formula.

The approach of Black et al. in 1996 represents an important methodological breakthrough. Rather than simply adjusting existing coefficients, these researchers adopted an allometric approach using fractional exponents, recognizing that relationships between body mass and metabolism are not strictly linear.

This innovation has proved particularly relevant for specific populations, such as the elderly and overweight, where traditional formulas have shown their limitations.

Choice of formula according to profile

The choice of the most appropriate formula depends essentially on the individual's profile and the context of use.

For a general population of healthy adults, the Mifflin-St Jeor or Roza-Shizgal formulas generally offer the best accuracy. These formulas, developed on samples more representative of modern populations, take better account of the morphological and nutritional changes that have occurred over the 20th century.

For people over 60, the Black et al. formula stands out for its ability to take account of age-related metabolic changes. Its allometric approach better captures the non-linear decrease in metabolism with age, offering more reliable estimates than traditional linear formulas.

For overweight and obese people, the Black et al. formula also offers significant advantages. Conventional formulas, developed mainly on normal-weight populations, tend to overestimate metabolism in people with excess body fat, as adipose tissue is metabolically less active than muscle tissue.

Limits of calculation models

First of all, each model has intrinsic limitations in common:

• Estimative character: all formulas give an estimate with a margin of error of ±10 to 20%.
• Reference populations: the formulas are based on specific samples which do not necessarily represent all human diversity.

In addition, there are many factors that are not taken into account:

• Individual hormonal variations
• Metabolic pathologies
• Plan history
• Precise body composition

In addition to these initial limitations, the specific situations of each individual must be taken into consideration in order to adjust the measurement:

• Athletes: metabolism can be significantly different due to the large muscle mass.
  
• Older people: age-related changes are only approximately modelled.
  
• Pathologies: hypothyroidism, diabetes, metabolic syndrome can distort estimates.
  
• Dieting history: people who have been on many diets may have a lower adapted metabolism.

In practical terms, the BMR can be used to give direction and a basis for work, but can never be used as an absolute truth.

• Use as a starting point: consider the BMR calculated as a base to be adjusted according to the results observed.
  
• Follow-up and adjustments: monitor weight trends over 2-3 weeks and adjust calorie intake accordingly.
  
• Holistic approach: take into account all factors: sleep, stress, physical activity, body composition.
  
• Professional consultation: if you have a specific pathology or objectives, consult a healthcare professional for a personalized approach.