Natural Metabolic Rate Calculator
.nmr-calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.nmr-header {
text-align: center;
margin-bottom: 30px;
}
.nmr-header h2 {
color: #2c3e50;
margin-bottom: 10px;
}
.nmr-form-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.nmr-form-grid {
grid-template-columns: 1fr;
}
}
.nmr-input-group {
margin-bottom: 15px;
}
.nmr-input-group label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #444;
}
.nmr-input-group input, .nmr-input-group select {
width: 100%;
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.nmr-input-group input:focus, .nmr-input-group select:focus {
border-color: #3498db;
outline: none;
}
.nmr-btn-container {
text-align: center;
margin-top: 20px;
grid-column: 1 / -1;
}
.nmr-calculate-btn {
background-color: #27ae60;
color: white;
padding: 15px 30px;
border: none;
border-radius: 5px;
font-size: 18px;
cursor: pointer;
transition: background 0.3s;
font-weight: bold;
}
.nmr-calculate-btn:hover {
background-color: #219150;
}
.nmr-results {
margin-top: 30px;
padding: 25px;
background: #fff;
border-left: 5px solid #3498db;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
display: none;
}
.nmr-result-item {
margin-bottom: 15px;
border-bottom: 1px solid #eee;
padding-bottom: 10px;
}
.nmr-result-item:last-child {
border-bottom: none;
}
.nmr-result-label {
font-size: 14px;
color: #7f8c8d;
text-transform: uppercase;
letter-spacing: 1px;
}
.nmr-result-value {
font-size: 28px;
color: #2c3e50;
font-weight: 800;
}
.nmr-result-desc {
font-size: 14px;
color: #555;
margin-top: 5px;
}
.nmr-highlight {
color: #e74c3c;
}
.nmr-article {
margin-top: 50px;
line-height: 1.6;
color: #333;
font-size: 16px;
}
.nmr-article h3 {
color: #2c3e50;
margin-top: 30px;
}
.nmr-article ul {
margin-bottom: 20px;
}
.nmr-article li {
margin-bottom: 8px;
}
.unit-toggle {
font-size: 0.9em;
color: #666;
margin-bottom: 5px;
display: block;
}
Basal Metabolic Rate (BMR)
—
Calories burned at complete rest.
Natural Daily Burn (TDEE)
—
Calories burned daily based on your activity level.
Weight Loss Zone
—
Recommended daily intake for sustainable weight loss (-500 cal).
Understanding Your Natural Metabolic Rate
Your "Natural Metabolic Rate," scientifically referred to as your Basal Metabolic Rate (BMR), represents the number of calories your body requires to perform basic life-sustaining functions. Even when you are sleeping, your body burns energy to pump blood, breathe, repair cells, and regulate body temperature. This calculator estimates that baseline number and adjusts it based on your lifestyle to determine your Total Daily Energy Expenditure (TDEE).
How the Calculation Works
This calculator utilizes the Mifflin-St Jeor equation, which is currently considered the standard for calculating metabolic rate due to its high accuracy in clinical settings. The formula takes into account four primary variables:
- Weight: Heavier bodies require more energy to maintain tissue and move.
- Height: Taller individuals generally have a larger body surface area and more lean mass, increasing metabolic demands.
- Age: As we age, metabolic rate naturally slows down, primarily due to a gradual loss of muscle mass.
- Gender: Men typically have more muscle mass and less body fat than women of the same weight, resulting in a higher BMR.
Interpreting Your Results
BMR (Basal Metabolic Rate): This is your "coma calories"—the amount you would burn if you stayed in bed all day without moving. You should rarely eat below this number, as doing so can trigger your body's starvation mode and slow your metabolism further.
TDEE (Total Daily Energy Expenditure): This is your maintenance level. It includes your BMR plus the calories burned through daily movement, exercise, and the thermic effect of food. If you eat at this number, your weight will likely stay the same.
Factors That Influence Natural Metabolism
While genetics play a role, you can influence your metabolic rate. Building lean muscle mass is the most effective way to increase your resting metabolic rate, as muscle tissue burns significantly more calories at rest than fat tissue does. Other factors include hormonal health (thyroid function), protein intake, and overall activity levels.
Using This Data for Goals
- For Weight Maintenance: Consume calories equal to your TDEE.
- For Weight Loss: Create a caloric deficit. A standard approach is to subtract 500 calories from your TDEE, aiming for approximately 1 lb of fat loss per week.
- For Muscle Gain: Create a slight surplus, typically 250-500 calories above your TDEE, combined with resistance training.
function updateNmrLabels() {
var unit = document.getElementById('nmr_unit').value;
var weightLabel = document.getElementById('label_weight');
var heightLabel = document.getElementById('label_height');
var weightInput = document.getElementById('nmr_weight');
var heightInput = document.getElementById('nmr_height');
var heightHelper = document.getElementById('height_helper');
if (unit === 'imperial') {
weightLabel.textContent = 'Weight (lbs)';
weightInput.placeholder = 'e.g. 150';
heightLabel.textContent = 'Height (inches)';
heightInput.placeholder = 'e.g. 70';
heightHelper.style.display = 'inline';
} else {
weightLabel.textContent = 'Weight (kg)';
weightInput.placeholder = 'e.g. 70';
heightLabel.textContent = 'Height (cm)';
heightInput.placeholder = 'e.g. 175';
heightHelper.style.display = 'none';
}
}
function calculateNaturalMetabolism() {
// Get input values
var gender = document.getElementById('nmr_gender').value;
var age = parseFloat(document.getElementById('nmr_age').value);
var unit = document.getElementById('nmr_unit').value;
var weightInput = parseFloat(document.getElementById('nmr_weight').value);
var heightInput = parseFloat(document.getElementById('nmr_height').value);
var activityMult = parseFloat(document.getElementById('nmr_activity').value);
// Validation
if (isNaN(age) || isNaN(weightInput) || isNaN(heightInput)) {
alert("Please enter valid numbers for Age, Weight, and Height.");
return;
}
var weightKg = 0;
var heightCm = 0;
// Convert units to Metric for Mifflin-St Jeor Formula
if (unit === 'imperial') {
// 1 lb = 0.453592 kg
weightKg = weightInput * 0.453592;
// 1 inch = 2.54 cm
heightCm = heightInput * 2.54;
} else {
weightKg = weightInput;
heightCm = heightInput;
}
// Calculate BMR (Mifflin-St Jeor Equation)
// Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
// Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
var bmr = 0;
if (gender === 'male') {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// Calculate TDEE
var tdee = bmr * activityMult;
// Calculate Weight Loss Target (-500 deficit)
var weightLossCal = tdee – 500;
// Safety check: Don't recommend below BMR or dangerous lows without warning
// For simplicity in this tool, we just display the math, but ensuring it's not negative
if (weightLossCal < 1200) {
// Optional: You could flag this, but we will just show the number
}
// Update DOM
document.getElementById('result_bmr').innerHTML = Math.round(bmr) + "
kcal/day";
document.getElementById('result_tdee').innerHTML = Math.round(tdee) + "
kcal/day";
document.getElementById('result_loss').innerHTML = Math.round(weightLossCal) + "
kcal/day";
// Show results
document.getElementById('nmr_results').style.display = 'block';
}