body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
}
.calculator-wrapper {
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-header {
text-align: center;
margin-bottom: 25px;
}
.calc-header h2 {
margin: 0;
color: #2c3e50;
}
.form-group {
margin-bottom: 20px;
}
.form-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #495057;
}
.form-row {
display: flex;
gap: 15px;
flex-wrap: wrap;
}
.col-half {
flex: 1;
min-width: 200px;
}
input[type="number"], select {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
input[type="radio"] {
margin-right: 5px;
}
.radio-group {
display: flex;
gap: 20px;
margin-bottom: 10px;
}
.radio-label {
font-weight: normal !important;
cursor: pointer;
display: flex;
align-items: center;
}
.unit-switch {
background: #e9ecef;
padding: 10px;
border-radius: 4px;
margin-bottom: 20px;
text-align: center;
}
.btn-calc {
background-color: #28a745;
color: white;
border: none;
padding: 15px 30px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
width: 100%;
transition: background-color 0.2s;
}
.btn-calc:hover {
background-color: #218838;
}
.results-area {
margin-top: 30px;
display: none;
background: white;
border: 1px solid #dee2e6;
border-radius: 8px;
padding: 20px;
}
.result-box {
text-align: center;
padding: 15px;
background: #f1f8e9;
border-radius: 6px;
margin-bottom: 15px;
}
.result-value {
font-size: 32px;
font-weight: 800;
color: #2e7d32;
display: block;
margin: 10px 0;
}
.result-label {
font-size: 14px;
text-transform: uppercase;
letter-spacing: 1px;
color: #555;
}
.metric-group, .imperial-group {
display: block;
}
.hidden {
display: none !important;
}
/* Article Styles */
.content-section {
margin-top: 50px;
}
h1 { font-size: 2.5em; margin-bottom: 0.5em; }
h2 { margin-top: 1.5em; color: #2c3e50; }
h3 { margin-top: 1.2em; color: #34495e; }
p { margin-bottom: 1.2em; color: #4a4a4a; }
ul { margin-bottom: 1.5em; padding-left: 20px; }
li { margin-bottom: 0.5em; }
.highlight-box {
background-color: #e3f2fd;
border-left: 5px solid #2196f3;
padding: 15px;
margin: 20px 0;
}
function toggleUnits() {
var isImperial = document.getElementById('unit-imperial').checked;
var wImp = document.getElementById('weight-imperial-input');
var wMet = document.getElementById('weight-metric-input');
var hImp = document.getElementById('height-imperial-input');
var hMet = document.getElementById('height-metric-input');
if (isImperial) {
wImp.className = ";
wMet.className = 'hidden';
hImp.className = 'form-row';
hMet.className = 'hidden';
document.getElementById('weight-label').innerText = "Weight (lbs)";
} else {
wImp.className = 'hidden';
wMet.className = ";
hImp.className = 'hidden';
hMet.className = ";
document.getElementById('weight-label').innerText = "Weight (kg)";
}
}
function calculateMetabolism() {
// Inputs
var age = parseFloat(document.getElementById('age').value);
var isMale = document.getElementById('gender-male').checked;
var activityMultiplier = parseFloat(document.getElementById('activity').value);
var isImperial = document.getElementById('unit-imperial').checked;
var weightKg = 0;
var heightCm = 0;
// Validation & Conversion
if (isNaN(age) || age < 1) {
alert("Please enter a valid age.");
return;
}
if (isImperial) {
var lbs = parseFloat(document.getElementById('weight-lbs').value);
var ft = parseFloat(document.getElementById('height-ft').value);
var inc = parseFloat(document.getElementById('height-in').value);
if (isNaN(lbs) || isNaN(ft) || isNaN(inc)) {
alert("Please fill in all weight and height fields.");
return;
}
// Convert to Metric for Formula
weightKg = lbs / 2.20462;
heightCm = ((ft * 12) + inc) * 2.54;
} else {
var kg = parseFloat(document.getElementById('weight-kg').value);
var cm = parseFloat(document.getElementById('height-cm').value);
if (isNaN(kg) || isNaN(cm)) {
alert("Please fill in all weight and height fields.");
return;
}
weightKg = kg;
heightCm = cm;
}
// Mifflin-St Jeor Equation
// Men: (10 × weight) + (6.25 × height) – (5 × age) + 5
// Women: (10 × weight) + (6.25 × height) – (5 × age) – 161
var bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age);
if (isMale) {
bmr = bmr + 5;
} else {
bmr = bmr – 161;
}
// Calculate TDEE
var tdee = bmr * activityMultiplier;
// Display Results
document.getElementById('bmr-result').innerText = Math.round(bmr).toLocaleString() + " kcal/day";
document.getElementById('tdee-result').innerText = Math.round(tdee).toLocaleString() + " kcal/day";
document.getElementById('results').style.display = 'block';
// Scroll to results
document.getElementById('results').scrollIntoView({behavior: "smooth"});
}
Most Accurate Metabolic Rate Calculator
Understanding your metabolic rate is the foundational step in any health, fitness, or weight management journey. This calculator utilizes the Mifflin-St Jeor equation, widely recognized by the Academy of Nutrition and Dietetics and clinical professionals as the most accurate formula for estimating Basal Metabolic Rate (BMR) in the general population.
What do the results mean?
Your BMR is the number of calories your body burns just to stay alive (breathing, circulation, cell production).
Your TDEE (Total Daily Energy Expenditure) accounts for your activity level. This is the amount of calories you need to eat to maintain your current weight.
How the Calculation Works
While there are several methods to calculate metabolic rate (such as the Harris-Benedict or Katch-McArdle equations), the Mifflin-St Jeor equation strikes the best balance between simplicity and accuracy for individuals without access to clinical metabolic testing equipment.
The Variables
Metabolism is not a static number; it fluctuates based on several biological factors used in this calculation:
- Weight: Larger bodies require more energy to function and move.
- Height: Taller individuals typically have a larger body surface area and higher BMR.
- Age: Metabolic rate tends to decrease by approximately 1-2% per decade after age 20 due to hormonal changes and muscle loss.
- Gender: Men generally have higher muscle mass and lower body fat percentages than women, leading to a higher BMR.
BMR vs. TDEE: What's the Difference?
It is crucial to distinguish between your Basal Metabolic Rate and your Total Daily Energy Expenditure when planning your diet.
Basal Metabolic Rate (BMR)
This is your "coma calories." If you laid in bed all day without moving, this is what your body would burn. Warning: You should rarely eat below your BMR, as this can trigger adaptive thermogenesis (starvation mode), where your body aggressively slows down metabolism to preserve energy.
Total Daily Energy Expenditure (TDEE)
This is your maintenance calorie number. It applies an "Activity Factor" to your BMR. Realistically, no one lies in bed 24/7. Even sedentary individuals walk to the car, type on a computer, or cook food. These activities burn calories via NEAT (Non-Exercise Activity Thermogenesis).
How to Use These Numbers
Once you have your TDEE from the calculator above, you can manipulate your intake to achieve your goals:
- To Lose Weight: Create a caloric deficit. A standard approach is to subtract 500 calories from your TDEE. This typically results in 1 lb (0.45 kg) of weight loss per week.
- To Gain Muscle: Create a caloric surplus. Add 250–500 calories to your TDEE to provide the energy required for muscle hypertrophy.
- To Maintain Weight: Eat according to your TDEE.
Improving Metabolic Accuracy
While this calculator provides a highly accurate estimate, your metabolism is adaptive. If you diet for a long time, your NEAT decreases, and your body becomes more efficient, effectively lowering your TDEE. Conversely, gaining muscle mass will increase your BMR over time, as muscle tissue is more metabolically active than fat tissue.
For the best results, use this calculator as a starting point. Track your weight and calorie intake for 2-3 weeks. If you are maintaining weight at a specific calorie intake, that is your true TDEE, regardless of what any calculator says.