Basal Metabolic Rate Calculator with Activity Level

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Basal Metabolic Rate (BMR) Calculator

Calculate your Basal Metabolic Rate (BMR), the number of calories your body needs to perform basic life-sustaining functions at rest. This calculator uses the Mifflin-St Jeor equation, which is considered one of the most accurate BMR estimation formulas.

Male Female
Sedentary (little to no exercise) Lightly active (exercise 1-3 days/week) Moderately active (exercise 3-5 days/week) Very active (exercise 6-7 days/week) Extra active (very intense exercise & physical job)
function calculateBMR() { var gender = document.getElementById("gender").value; var weightKg = parseFloat(document.getElementById("weightKg").value); var heightCm = parseFloat(document.getElementById("heightCm").value); var age = parseFloat(document.getElementById("age").value); var activityLevel = parseFloat(document.getElementById("activityLevel").value); var resultDiv = document.getElementById("result"); if (isNaN(weightKg) || isNaN(heightCm) || isNaN(age) || weightKg <= 0 || heightCm <= 0 || age <= 0) { resultDiv.innerHTML = "Please enter valid positive numbers for weight, height, and age."; return; } var bmr = 0; if (gender === "male") { bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5; } else { // female bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161; } var totalDailyCalories = bmr * activityLevel; resultDiv.innerHTML = "Your Basal Metabolic Rate (BMR) is approximately " + bmr.toFixed(2) + " calories per day. " + "To maintain your current weight with your activity level, you need approximately " + totalDailyCalories.toFixed(2) + " calories per day."; }

Understanding Basal Metabolic Rate (BMR)

Your Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to function at rest. This includes essential processes like breathing, circulation, cell production, and nutrient processing. Think of it as the energy your body expends just to keep you alive if you were to spend the entire day completely inactive.

Factors Affecting BMR

  • Body Composition: Muscle tissue burns more calories at rest than fat tissue. Therefore, individuals with higher muscle mass generally have a higher BMR.
  • Age: BMR tends to decrease with age, as muscle mass often declines.
  • Sex: Men typically have a higher BMR than women due to generally larger body size and a higher proportion of muscle mass.
  • Genetics: Individual genetic makeup can play a role in metabolic rate.
  • Body Size and Shape: Larger individuals generally have higher BMRs.
  • Hormones: Thyroid hormones, in particular, significantly influence metabolism.

The Mifflin-St Jeor Equation

The Mifflin-St Jeor equation is widely recognized as a reliable method for estimating BMR. The formulas are:

  • 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

Activity Level Multipliers

Your BMR is the energy expenditure at rest. To determine your total daily energy expenditure (TDEE), you need to factor in your physical activity. The calculator uses multipliers based on your self-assessed activity level:

  • Sedentary: Little to no exercise. Multiply BMR by 1.2.
  • Lightly Active: Exercise 1-3 days per week. Multiply BMR by 1.375.
  • Moderately Active: Exercise 3-5 days per week. Multiply BMR by 1.55.
  • Very Active: Exercise 6-7 days per week. Multiply BMR by 1.725.
  • Extra Active: Very intense exercise and a physical job. Multiply BMR by 1.9.

By multiplying your BMR by the appropriate activity factor, you get an estimate of the total calories you need to consume daily to maintain your current weight.

Example Calculation

Let's calculate the BMR and TDEE for a 30-year-old male who weighs 75 kg, is 180 cm tall, and is moderately active.

  • Gender: Male
  • Weight: 75 kg
  • Height: 180 cm
  • Age: 30 years
  • Activity Level: Moderately active (multiplier = 1.55)

Using the Mifflin-St Jeor equation for men:

BMR = (10 × 75) + (6.25 × 180) – (5 × 30) + 5

BMR = 750 + 1125 – 150 + 5

BMR = 1730 calories per day

Now, calculating the Total Daily Calories (TDEE):

TDEE = BMR × Activity Level Multiplier

TDEE = 1730 × 1.55

TDEE = 2681.5 calories per day

So, this individual needs approximately 1730 calories to maintain basic bodily functions at rest and about 2681.5 calories per day to maintain their current weight given their activity level.

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