What Is BMR?

BMR stands for Basal Metabolic Rate. It is an estimate of the amount of energy your body uses each day while at rest to maintain essential physiological functions.

These functions include:

• Breathing;
• Blood circulation;
• Brain activity;
• Temperature regulation;
• Cellular processes; and
• Basic organ function.

How Is BMR Calculated?

This calculator uses the Mifflin–St Jeor equation as the primary BMR formula.

Male Mifflin–St Jeor formula

Female Mifflin–St Jeor formula

BMR Calculation Example

For a 30-year-old male weighing 75 kg and measuring 175 cm:

BMR vs TDEE

BMR and TDEE are related but represent different things.

BMR

BMR estimates the energy required to support basic body functions at rest.

TDEE

TDEE stands for Total Daily Energy Expenditure and includes estimated energy used through physical activity and everyday movement.

For a more complete estimate of daily energy needs, use the TDEE Calculator.

Does BMR Include Exercise?

No. BMR is intended to estimate resting energy use and does not include exercise calories.

Exercise and daily activity are considered when estimating TDEE.

Does BMR Include Walking and Daily Movement?

No. Everyday movement is not included directly in basal metabolic rate.

Daily energy expenditure can also include:

• Walking;
• Work activity;
• Household movement;
• Exercise;
• Digesting food; and
• Other activity above rest.

Why Does BMR Change With Age?

BMR equations include age because average energy requirements tend to change over the lifespan.

Body composition can also change with age, including changes in lean mass, which may influence resting energy expenditure.

Why Does Body Weight Affect BMR?

Larger bodies generally require more energy to maintain basic functions. This is why body weight is included in common BMR equations.

However, two people of the same body weight can still have different actual resting energy expenditure because of differences in body composition and other factors.

Why Does Height Affect BMR?

Height is used as a rough indicator of body size in population-based equations.

All else equal, a taller body generally has more tissue to maintain than a shorter body.

Why Do Male and Female BMR Formulas Differ?

The standard Mifflin–St Jeor formula uses different constants for male and female calculations because the original equations were developed from population data with average body-composition differences.

What Is the Harris-Benedict Equation?

The Harris-Benedict equation is another commonly known method for estimating basal or resting energy needs from age, sex, height and weight.

This calculator shows both a revised Harris-Benedict estimate and the older original Harris-Benedict estimate for comparison.

Why Do Different BMR Formulas Give Different Results?

BMR equations were developed from different research populations and statistical models.

As a result, Mifflin–St Jeor, Harris-Benedict and other equations can produce slightly different estimates for the same person.

How Accurate Is a BMR Calculator?

A BMR calculator can provide a useful starting estimate, but actual energy needs vary between individuals.

Factors that may affect resting energy expenditure include:

• Lean body mass;
• Body size;
• Genetics;
• Age;
• Hormonal factors;
• Health conditions;
• Medications;
• Pregnancy;
• Temperature; and
• Individual metabolic variation.

Can BMR Tell Me How Many Calories to Eat?

Not by itself.

BMR represents estimated resting energy use and is generally lower than total daily energy expenditure.

If you want an estimate of maintenance calories, use BMR together with an activity factor or use the TDEE Calculator.

Should I Eat Below My BMR to Lose Weight?

BMR should not automatically be treated as a calorie-intake target. It is an estimate of resting energy expenditure, not a personalised minimum safe intake.

Appropriate calorie intake depends on total energy needs, nutritional requirements, health status and individual goals.

BMR and Weight Loss

BMR can help provide context when estimating overall energy needs, but weight change depends on energy intake relative to total energy expenditure, not BMR alone.

For weight-management planning:

• Estimate BMR;
• Estimate TDEE;
• Compare average energy intake with expenditure; and
• Track results over time.

BMR and Muscle Mass

Lean tissue generally uses more energy than fat tissue, so body composition can affect resting energy expenditure.

Standard BMR equations do not directly measure muscle mass.

If you want to estimate body composition, use the Body Fat Calculator.

BMR and Kilojoules

In Australia, food energy is commonly shown in kilojoules.

One dietary kilocalorie is approximately:

The calculator automatically converts the BMR estimate into kilojoules.

Can BMR Be Used During Pregnancy?

Standard BMR equations do not fully account for the physiological and energy changes associated with pregnancy.

Pregnancy nutrition needs should not be determined solely from a standard BMR calculator.

Can Teenagers Use This BMR Calculator?

This calculator is intended primarily for adults.

Children and adolescents have energy needs related to growth and development, so age-specific methods may be more appropriate.

BMR Calculator Assumptions

This calculator:

• Uses the Mifflin–St Jeor equation for the main result;
• Also displays Harris-Benedict estimates for comparison;
• Supports metric and imperial measurements;
• Converts imperial measurements internally to kilograms and centimetres;
• Estimates resting energy expenditure rather than measuring it;
• Does not include physical activity;
• Does not directly account for body-fat percentage;
• Does not calculate personalised nutritional requirements;
• Is intended primarily for adults; and
• Does not provide a medical diagnosis.

Related Health & Fitness Calculators