Sedentary (little or 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 a week)
Extra active (very hard exercise/sports & physical job or 2x training)
Enter your details to calculate.
Understanding BMI and Its Role in Weight Loss
The Body Mass Index (BMI) is a widely used screening tool to categorize a person's weight status relative to their height. It's a simple, non-invasive method to estimate body fat and identify potential weight categories that may pose health risks. While BMI doesn't directly measure body fat, it correlates well with more direct measures for most individuals.
How BMI is Calculated
The formula for BMI is: Weight (kg) / [Height (m)]².
To simplify calculations and provide more comprehensive insights, our calculator also incorporates factors like age, gender, and activity level to estimate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE).
BMI Calculation (as performed by the calculator):
Height is converted from centimeters to meters (cm / 100).
BMI = Weight (kg) / (Height (m) * Height (m))
Understanding Your BMI Results
Your BMI falls into one of several categories:
Underweight: Below 18.5
Normal weight: 18.5 – 24.9
Overweight: 25 – 29.9
Obesity Class I: 30 – 34.9
Obesity Class II: 35 – 39.9
Obesity Class III: 40 and above
Basal Metabolic Rate (BMR)
BMR is the number of calories your body needs to perform basic life-sustaining functions at rest, such as breathing, circulation, and cell production. A higher BMR means your body burns more calories even when you're not active.
Our calculator uses the Mifflin-St Jeor Equation, which is considered one of the most accurate formulas:
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
Total Daily Energy Expenditure (TDEE)
TDEE is the total number of calories you burn in a day, including your BMR and any calories burned through physical activity and digestion. It's a crucial metric for weight management.
TDEE is calculated by multiplying your BMR by an activity factor:
TDEE = BMR × Activity Level Factor
The activity factors used are standard estimates:
Sedentary: 1.2
Lightly active: 1.375
Moderately active: 1.55
Very active: 1.725
Extra active: 1.9
Using BMI and TDEE for Weight Loss
To lose weight, you need to consume fewer calories than your body burns, creating a calorie deficit. Your TDEE represents your estimated daily calorie burn.
* Calorie Deficit for Weight Loss: A common recommendation is to aim for a deficit of 500-1000 calories per day to lose 1-2 pounds per week. This means consuming TDEE – 500 to TDEE – 1000 calories daily.
* Maintaining Weight: To maintain your current weight, aim to consume calories close to your TDEE.
* Gaining Weight: To gain weight, you would need to consume more calories than your TDEE.
Important Note: BMI is a starting point. It does not account for muscle mass, bone density, or body composition. Athletes, for instance, may have a high BMI due to muscle mass but still be healthy. Always consult with a healthcare professional or registered dietitian for personalized weight management advice and health assessments.
function calculateBMI() {
var weight = document.getElementById("weight").value;
var heightCm = document.getElementById("height").value;
var age = document.getElementById("age").value;
var gender = document.getElementById("gender").value;
var activityLevel = document.getElementById("activityLevel").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = 'Enter your details to calculate.'; // Reset previous result
var errors = [];
if (isNaN(weight) || weight <= 0) errors.push("Weight must be a positive number.");
if (isNaN(heightCm) || heightCm <= 0) errors.push("Height must be a positive number in cm.");
if (isNaN(age) || age 0) {
resultDiv.innerHTML = " + errors.join(") + ";
return;
}
var heightM = heightCm / 100;
var bmi = weight / (heightM * heightM);
bmi = bmi.toFixed(1);
var bmiCategory = "";
var bmiColor = "#333";
if (bmi = 18.5 && bmi = 25 && bmi = 30 && bmi = 35 && bmi <= 39.9) {
bmiCategory = "Obesity Class II";
bmiColor = "#dc3545"; // Danger red
} else {
bmiCategory = "Obesity Class III";
bmiColor = "#dc3545"; // Danger red
}
// Calculate BMR using Mifflin-St Jeor Equation
var bmr = 0;
if (gender === "male") {
bmr = (10 * weight) + (6.25 * heightCm) – (5 * age) + 5;
} else {
bmr = (10 * weight) + (6.25 * heightCm) – (5 * age) – 161;
}
bmr = bmr.toFixed(0);
// Calculate TDEE
var tdee = bmr * parseFloat(activityLevel);
tdee = tdee.toFixed(0);
var weightLossTarget = (tdee – 500).toFixed(0);
var weightGainTarget = (parseFloat(tdee) + 500).toFixed(0);
resultDiv.innerHTML = `
Your BMI: ${bmi} (${bmiCategory})
Estimated BMR: ${bmr} calories/day
Estimated TDEE: ${tdee} calories/day
To lose weight (approx. 1 lb/week), aim for ~${weightLossTarget} calories/day.
To gain weight (approx. 1 lb/week), aim for ~${weightGainTarget} calories/day.
`;
}