Basal Metabolic Rate (BMR) Calculator
Your Basal Metabolic Rate (BMR)
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;
var resultDiv = document.getElementById("result");
var explanationDiv = document.getElementById("bmr-explanation");
if (isNaN(weight) || isNaN(height) || isNaN(age)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
explanationDiv.innerHTML = "";
return;
}
if (gender === "male") {
// Mifflin-St Jeor Equation for Men
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else {
// Mifflin-St Jeor Equation for Women
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
}
if (bmr < 0) {
resultDiv.innerHTML = "Calculation resulted in a negative BMR. Please check your inputs.";
explanationDiv.innerHTML = "";
} else {
resultDiv.innerHTML = bmr.toFixed(2) + " kcal/day";
explanationDiv.innerHTML = "Your Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to maintain basic life functions like breathing, circulation, and cell production. This value is an estimate and can vary based on factors like muscle mass, body composition, and genetics.";
}
}
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #e0e0e0;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
background-color: #fff;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 25px;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
gap: 15px;
margin-bottom: 25px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 8px;
font-weight: bold;
color: #555;
}
.input-group input[type="number"],
.input-group select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
width: 100%;
box-sizing: border-box;
}
.calculator-inputs button {
grid-column: 1 / -1;
padding: 12px 20px;
background-color: #4CAF50;
color: white;
border: none;
border-radius: 4px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-inputs button:hover {
background-color: #45a049;
}
.calculator-results {
text-align: center;
border-top: 1px solid #eee;
padding-top: 20px;
}
.calculator-results h3 {
color: #4CAF50;
margin-bottom: 15px;
}
#result {
font-size: 1.8rem;
font-weight: bold;
color: #333;
margin-bottom: 10px;
}
#bmr-explanation {
font-size: 0.95rem;
color: #666;
line-height: 1.5;
}
## Understanding Your Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to function at rest. Think of it as the energy expenditure required to keep your vital organs running – your heart beating, lungs breathing, brain functioning, and maintaining body temperature, all while you're in a completely relaxed state, such as when you're asleep. It's the baseline energy cost for survival.
The BMR is influenced by several factors, including:
* **Age:** As we age, our metabolism tends to slow down.
* **Gender:** Men generally have a higher BMR than women due to typically having more muscle mass.
* **Body Weight and Composition:** Muscle tissue burns more calories at rest than fat tissue. Therefore, individuals with more muscle mass tend to have a higher BMR.
* **Height:** Taller individuals often have a higher BMR.
* **Genetics:** Individual metabolic rates can vary due to genetic predispositions.
* **Hormonal Levels:** Conditions affecting thyroid hormones, for instance, can significantly impact BMR.
* **Environmental Temperature:** Extreme temperatures can slightly increase BMR as the body works to maintain its core temperature.
### The Mifflin-St Jeor Equation
The calculator above uses the Mifflin-St Jeor equation, which is widely considered one of the most accurate formulas for estimating BMR. It was developed in 1990 and is preferred over older equations like the Harris-Benedict for its improved accuracy.
**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
### How BMR Relates to Your Daily Calorie Needs
Your BMR is just one piece of the puzzle when it comes to your total daily energy expenditure (TDEE). Your TDEE is the total number of calories you burn in a day, including your BMR plus the calories burned through physical activity, digestion (the thermic effect of food), and any other daily movements.
To maintain your current weight, you would generally aim to consume calories close to your TDEE. If you wish to lose weight, you'd need to consume fewer calories than your TDEE (create a calorie deficit). Conversely, to gain weight, you'd consume more calories than your TDEE (create a calorie surplus). Your BMR provides the fundamental number upon which these calculations are based.