How to Calculate the Basal Metabolic Rate

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Basal Metabolic Rate (BMR) Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions, such as breathing, circulation, and cell production, while at rest. It's essentially the energy expenditure of your body at complete rest in a temperate environment, in a post-absorptive state. Knowing your BMR is a crucial first step in understanding your daily calorie needs for weight management and overall health.

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Understanding Your BMR

The Basal Metabolic Rate (BMR) is the minimum amount of energy your body requires to maintain basic physiological functions. These functions include breathing, maintaining body temperature, circulating blood, and the operation of your brain and nervous system. Since these processes are continuous, your BMR accounts for a significant portion of your total daily energy expenditure, even if you lead a sedentary lifestyle.

Factors Influencing BMR:

  • Body Composition: Muscle tissue burns more calories at rest than fat tissue. Therefore, individuals with a higher muscle mass generally have a higher BMR.
  • Age: BMR typically decreases with age, as muscle mass tends to decline and metabolic processes slow down.
  • Sex: Men generally have a higher BMR than women due to typically having more muscle mass and a higher body fat percentage.
  • Genetics: Your inherited genes play a role in determining your metabolic rate.
  • Body Size and Shape: Larger individuals generally have a higher BMR.
  • Hormone Levels: Hormones like thyroid hormones significantly influence metabolism.
  • Environmental Temperature: Extreme temperatures can increase BMR as the body works harder to maintain its core temperature.

How BMR is Calculated:

The most common formulas for calculating BMR are the Harris-Benedict Equation and the Mifflin-St Jeor Equation. The Mifflin-St Jeor Equation is generally considered more accurate for most people.

Mifflin-St Jeor Equation:

  • 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

This calculator uses the Mifflin-St Jeor Equation. Once you have your BMR, you can estimate your Total Daily Energy Expenditure (TDEE) by multiplying your BMR by an activity factor that corresponds to your lifestyle.

function calculateBMR() { var gender = document.getElementById("gender").value; var weight = parseFloat(document.getElementById("weight").value); var height = parseFloat(document.getElementById("height").value); var age = parseFloat(document.getElementById("age").value); var bmr = 0; if (isNaN(weight) || isNaN(height) || isNaN(age) || weight <= 0 || height <= 0 || age <= 0) { document.getElementById("bmr-result").innerHTML = "Please enter valid positive numbers for weight, height, and age."; return; } if (gender === "male") { bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5; } else { // female bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161; } document.getElementById("bmr-result").innerHTML = "Your estimated Basal Metabolic Rate (BMR) is: " + bmr.toFixed(2) + " calories per day"; }

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