Sedentary (little to no exercise)
Lightly Active (light exercise/sports 1-3 days/week)
Moderately Active (moderate exercise/sports 3-5 days/week)
Very Active (hard exercise/sports 6-7 days/week)
Extra Active (very hard exercise/sports & physical job or 2x training)
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}
.calculator-container h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.inputs-section {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.form-group {
display: flex;
flex-direction: column;
}
.form-group label {
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.form-group input[type="number"],
.form-group select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
.form-group input[type="number"]:focus,
.form-group select:focus {
outline: none;
border-color: #007bff;
box-shadow: 0 0 0 2px rgba(0,123,255,0.25);
}
button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
}
button:hover {
background-color: #0056b3;
}
.result-section {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
font-size: 1.1rem;
color: #495057;
}
.result-section p {
margin: 5px 0;
}
.result-section span {
font-weight: bold;
}
var activityFactors = {
sedentary: 1.2,
lightly_active: 1.375,
moderately_active: 1.55,
very_active: 1.725,
extra_active: 1.9
};
function calculateMetabolicRate() {
var gender = document.getElementById("gender").value;
var age = parseInt(document.getElementById("age").value);
var weight = parseInt(document.getElementById("weight").value);
var height = parseInt(document.getElementById("height").value);
var bodyFatPercentage = parseInt(document.getElementById("bodyFatPercentage").value);
var activityLevel = document.getElementById("activityLevel").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(age) || isNaN(weight) || isNaN(height) || isNaN(bodyFatPercentage) ||
age <= 0 || weight <= 0 || height <= 0 || bodyFatPercentage 100) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields, and a body fat percentage between 0 and 100.";
return;
}
var bmr;
// Mifflin-St Jeor Equation (commonly used and accounts for body composition better with body fat)
if (gender === "male") {
// BMR = (10 * weight in kg) + (6.25 * height in cm) – (5 * age in years) + 5
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else { // female
// BMR = (10 * weight in kg) + (6.25 * height in cm) – (5 * age in years) – 161
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
}
// Adjusting BMR based on body fat percentage if available and within reasonable range
// This is a simplified adjustment. More complex models exist.
// For example, a higher body fat percentage generally means lower lean body mass, thus lower BMR.
// We'll assume lean body mass is (1 – bodyFatPercentage/100) * totalWeight
// And that fat mass has a lower metabolic rate than lean mass.
// A common estimate is that fat tissue burns ~4.5 kcal/kg/day, and lean tissue ~13 kcal/kg/day.
var fatMass = weight * (bodyFatPercentage / 100);
var leanMass = weight – fatMass;
// Calculate BMR based on lean and fat mass components
// BMR_lean = leanMass (kg) * 13 kcal/kg/day
// BMR_fat = fatMass (kg) * 4.5 kcal/kg/day
// BMR_adjusted = BMR_lean + BMR_fat
var bmr_adjusted_by_fat = (leanMass * 13) + (fatMass * 4.5);
// Decide whether to use the standard Mifflin-St Jeor or the body-fat adjusted one.
// Often, if body fat is known and within a reasonable range (e.g., not extremely low or high,
// which might indicate an error in measurement or a special condition), the adjusted one is preferred.
// For simplicity here, we'll use the adjusted one if body fat is provided and valid.
var finalBmr = bmr_adjusted_by_fat;
var activityFactor = activityFactors[activityLevel];
if (!activityFactor) {
resultDiv.innerHTML = "Invalid activity level selected.";
return;
}
var tdee = finalBmr * activityFactor;
resultDiv.innerHTML =
"Basal Metabolic Rate (BMR) (adjusted for body fat): " + finalBmr.toFixed(2) + " kcal/day" +
"Total Daily Energy Expenditure (TDEE): " + tdee.toFixed(2) + " kcal/day";
}
Understanding Your Metabolic Rate and Body Composition
Your metabolic rate is the total number of calories your body burns in a 24-hour period. It's a crucial factor in understanding weight management, energy levels, and overall health. Two key components of your metabolic rate are your Basal Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE).
Basal Metabolic Rate (BMR)
BMR represents the minimum number of calories your body needs to perform essential life-sustaining functions at rest. This includes breathing, circulation, cell production, and brain activity. Think of it as the energy your body burns just to keep you alive if you were to sleep all day.
Factors influencing BMR include:
Age: BMR generally decreases with age.
Gender: Men typically have a higher BMR than women due to differences in body composition (more muscle mass).
Body Weight and Height: Larger individuals generally have higher BMRs.
Body Composition (Lean Mass vs. Fat Mass): This is where body fat percentage becomes critical. Muscle tissue is metabolically more active than fat tissue. Therefore, individuals with a higher percentage of lean body mass (muscle, bone, organs) will have a higher BMR than individuals of the same weight with a higher percentage of body fat.
Total Daily Energy Expenditure (TDEE)
TDEE takes your BMR and adds the calories burned through all your daily activities. This includes:
Thermic Effect of Food (TEF): The calories your body burns digesting and absorbing food.
Physical Activity: Calories burned through planned exercise (like going to the gym or running) and non-exercise activity thermogenesis (NEAT), which includes everyday movements like walking, fidgeting, and standing.
Your TDEE is the most accurate reflection of how many calories you burn daily. To maintain your current weight, your calorie intake should match your TDEE. To lose weight, you need to consume fewer calories than your TDEE (a calorie deficit). To gain weight, you need to consume more calories than your TDEE (a calorie surplus).
How Body Fat Percentage Impacts BMR
While standard BMR formulas are useful, incorporating body fat percentage provides a more personalized and accurate estimation. The Mifflin-St Jeor equation is a widely accepted formula. However, it doesn't directly account for body composition. When you know your body fat percentage, you can estimate the contribution of your lean body mass (muscle, bones, organs) and fat mass to your overall metabolism. Lean body mass is significantly more metabolically active than fat mass. By adjusting for this, we can get a more precise BMR, which in turn leads to a more accurate TDEE calculation.
Using This Calculator
This calculator uses the Mifflin-St Jeor equation as a baseline and then adjusts the BMR calculation based on your provided body fat percentage, assuming typical metabolic rates for lean and fat tissue. It then multiplies this adjusted BMR by an activity factor corresponding to your chosen lifestyle to estimate your TDEE.
Example:
Consider a 35-year-old male who weighs 80 kg, is 180 cm tall, has 20% body fat, and considers himself moderately active.
Gender: Male
Age: 35 years
Weight: 80 kg
Height: 180 cm
Body Fat Percentage: 20%
Activity Level: Moderately Active
First, we calculate lean mass and fat mass:
Fat Mass = 80 kg * (20 / 100) = 16 kg
Lean Mass = 80 kg – 16 kg = 64 kg
Then, we estimate BMR based on these masses (using typical kcal/kg values for lean and fat tissue):
BMR (Lean Mass Contribution) = 64 kg * 13 kcal/kg/day = 832 kcal/day
BMR (Fat Mass Contribution) = 16 kg * 4.5 kcal/kg/day = 72 kcal/day
Adjusted BMR = 832 + 72 = 904 kcal/day
For a moderately active individual, the activity factor is 1.55.
TDEE = Adjusted BMR * Activity Factor
TDEE = 904 kcal/day * 1.55 = 1401.2 kcal/day
This suggests that this individual needs approximately 1401.2 calories per day to maintain his current weight, based on his body composition and activity level.
Remember, these are estimations. Individual metabolisms can vary. For precise dietary and exercise plans, consulting with a healthcare professional or a registered dietitian is recommended.