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Basal Metabolic Rate (BMR) Calculator

Developed & Reviewed by: Nutrify Team

Last updated: October 26, 2024

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What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) is the number of calories your body burns while at complete rest to maintain basic life functions. These functions include breathing, circulating blood, organ functions, and basic neurological functions. BMR is measured under very strict conditions: after a full night's sleep, in a fasted state, and in a neutral temperature environment.

Understanding your BMR is crucial for managing your weight and overall health. It forms the foundation of your daily calorie needs, to which calories burned through physical activity and digestion are added.

BMR Calculation Formulas

Our calculator offers four different formulas to estimate your BMR:

  • Mifflin-St Jeor Equation: Considered one of the most accurate for a general population.
  • Harris-Benedict Equation: One of the earliest and still widely used formulas.
  • Katch-McArdle Formula: Takes into account lean body mass, which can be more accurate for athletic individuals.
  • Schofield Equation: Uses different calculations based on age groups and gender.

Each formula may be more suitable for different individuals based on factors like age, body composition, and activity level.

Understanding BMR Formulas

Let's compare how each formula calculates BMR using the same example person:

Example Person:

  • Gender: Female
  • Age: 30 years
  • Height: 165 cm (5'5")
  • Weight: 60 kg (132 lbs)
  • Body Fat: 25%
  • Lean Body Mass: 45 kg

1. Mifflin-St Jeor Equation

The most widely recommended formula for the general population.

Formula:

For women: (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

Calculation:

(10 × 60) + (6.25 × 165) - (5 × 30) - 161

= 600 + 1031.25 - 150 - 161

= 1,320 calories/day

2. Harris-Benedict Equation

One of the oldest and most established formulas.

Formula:

For women: 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) - (4.676 × age)

Calculation:

655.1 + (9.563 × 60) + (1.850 × 165) - (4.676 × 30)

= 655.1 + 573.78 + 305.25 - 140.28

= 1,394 calories/day

3. Katch-McArdle Formula

Best for athletic individuals as it uses lean body mass.

Formula:

370 + (21.6 × lean body mass in kg)

Calculation:

370 + (21.6 × 45)

= 370 + 972

= 1,342 calories/day

4. Schofield Equation

Uses age-specific calculations recommended by WHO.

Formula for women (18-30 years):

14.818 × weight in kg + 486.6

Calculation:

(14.818 × 60) + 486.6

= 889.08 + 486.6

= 1,376 calories/day

Key Observations:

  • Results vary by up to 74 calories between formulas
  • Mifflin-St Jeor gives the most conservative estimate
  • Harris-Benedict typically estimates slightly higher
  • Katch-McArdle is useful when body fat percentage is known
  • Schofield is particularly good for age-specific calculations

Factors Affecting BMR

Several factors can influence your BMR:

  • Age: BMR typically decreases with age
  • Gender: Men generally have a higher BMR than women
  • Body composition: More muscle mass increases BMR
  • Genetics: Some people naturally have a higher or lower BMR
  • Hormones: Thyroid hormones, for example, can affect BMR
  • Diet: Severe calorie restriction can lower BMR
  • Environmental temperature: Extreme cold or heat can increase BMR

Using Your BMR Results

Once you know your BMR, you can use it to:

  • Set realistic weight loss or gain goals
  • Create an effective meal plan
  • Understand how many calories you need for different activity levels
  • Make informed decisions about your diet and exercise routine

Remember, BMR is just one part of the equation. To maintain weight, you need to consume the same number of calories as you burn through BMR, physical activity, and the thermic effect of food. To lose weight, you need to create a calorie deficit, and to gain weight, a calorie surplus.

How to Use This Calculator

  1. Enter your age in years
  2. Select your gender
  3. Enter your height (you can choose between cm, feet, or inches)
  4. Enter your weight (you can choose between kg or lbs)
  5. Select your preferred BMR formula
  6. Click the Calculate BMR button
  7. Review your results, including your BMR and daily calorie needs for different activity levels

Remember, while this calculator provides a good estimate, individual BMR can vary. For the most accurate measurement, consider professional testing methods like indirect calorimetry.

FAQ

Frequently Asked Questions

Find answers to common questions

  • BMR stands for Basal Metabolic Rate. It's the number of calories your body burns at complete rest to maintain basic life functions like breathing, circulating blood, and regulating body temperature.

  • The Schofield equation is a widely-used formula for calculating BMR that takes into account age groups and gender. It was developed based on a large dataset and is particularly accurate for different age ranges, making it popular in clinical and research settings.

  • BMR (Basal Metabolic Rate) and RMR (Resting Metabolic Rate) are similar but measured under slightly different conditions. BMR is measured in a more controlled environment after fasting and complete rest. RMR is typically slightly higher than BMR but is easier to measure.

  • The Schofield equation is considered highly accurate, especially for people within standard weight ranges. It was developed using data from over 11,000 individuals and is recommended by the WHO and other health organizations for BMR calculations.

  • The Schofield equation provides specific calculations for different age groups: 0-3 years, 3-10 years, 10-18 years, 18-30 years, 30-60 years, and over 60 years. This makes it particularly versatile for people of all ages.

  • Your Schofield BMR result can be used to determine your total daily energy expenditure (TDEE) by applying an activity factor. This helps in planning nutrition, weight management, and fitness goals with age-appropriate considerations.

  • The accuracy of BMR formulas can vary depending on individual factors. The Mifflin-St Jeor equation is often considered the most accurate for a general population, but the best formula may depend on your specific characteristics.

  • Your BMR can be used as a starting point to determine your total daily energy expenditure (TDEE). By factoring in your activity level, you can estimate how many calories you need to maintain, lose, or gain weight.

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