Fitness Calorie Calculator
Use this calculator to estimate your daily calorie needs based on your age, gender, weight, height, activity level, and fitness goals. Understanding your caloric intake is crucial for weight management, whether you aim to lose, maintain, or gain weight.
Understanding Your Calorie Needs
Your body requires a certain amount of energy, measured in calories, to perform basic functions like breathing, circulation, and cell repair (Basal Metabolic Rate – BMR), as well as for all physical activities. This calculator uses the Mifflin-St Jeor equation, which is widely recognized for its accuracy in estimating BMR.
Basal Metabolic Rate (BMR)
BMR is the number of calories your body burns at rest to maintain vital functions. It's influenced by factors such as age, gender, weight, and height. Generally, men tend to have a higher BMR than women due to differences in muscle mass and body composition. As you age, your BMR typically decreases.
Total Daily Energy Expenditure (TDEE)
Your TDEE is your BMR multiplied by an activity factor. This factor accounts for the calories you burn through exercise and daily movement. The more active you are, the higher your TDEE will be. The calculator provides different activity levels, from sedentary to extra active, to help you accurately estimate your TDEE.
Fitness Goals and Calorie Adjustment
- Maintain Weight: If your goal is to maintain your current weight, your daily calorie intake should roughly match your TDEE.
- Weight Loss: To lose weight, you need to create a calorie deficit, meaning you consume fewer calories than your body burns. A deficit of 500 calories per day typically leads to a loss of about 0.5 kg (1 pound) per week. This calculator offers options for mild, moderate, and extreme weight loss, adjusting your TDEE accordingly.
- Weight Gain: To gain weight, particularly muscle mass, you need to consume more calories than your body burns, creating a calorie surplus. Similar to weight loss, this calculator provides options for mild, moderate, and extreme weight gain.
Important Considerations
While this calculator provides a good estimate, individual calorie needs can vary based on genetics, body composition, metabolic health, and other factors. It's always recommended to consult with a healthcare professional or a registered dietitian for personalized advice, especially if you have underlying health conditions or are planning significant dietary changes. This calculator is for informational purposes only and should not replace professional medical advice.
Example Calculation:
Let's say we have a 30-year-old male, weighing 70 kg, 175 cm tall, moderately active, and aiming to maintain weight.
- Age: 30 years
- Gender: Male
- Weight: 70 kg
- Height: 175 cm
- Activity Level: Moderately Active (multiplier 1.55)
- Goal: Maintain Weight
Using the Mifflin-St Jeor formula for men:
BMR = (10 × 70) + (6.25 × 175) – (5 × 30) + 5
BMR = 700 + 1093.75 – 150 + 5 = 1648.75 calories
TDEE = BMR × Activity Level = 1648.75 × 1.55 = 2555.56 calories
For maintaining weight, the recommended daily calorie intake would be approximately 2556 calories.
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function calculateCalories() {
var age = parseFloat(document.getElementById("age").value);
var weight = parseFloat(document.getElementById("weight").value);
var height = parseFloat(document.getElementById("height").value);
var genderMale = document.getElementById("genderMale").checked;
var activityLevelMultiplier = parseFloat(document.getElementById("activityLevel").value);
var goal = document.getElementById("goal").value;
var weightUnit = document.getElementById("weightUnit").value;
var heightUnit = document.getElementById("heightUnit").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(age) || age <= 0 || isNaN(weight) || weight <= 0 || isNaN(height) || height <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for age, weight, and height.";
return;
}
// Convert units to metric for Mifflin-St Jeor
var weightKg = weight;
if (weightUnit === "lbs") {
weightKg = weight * 0.453592;
}
var heightCm = height;
if (heightUnit === "inches") {
heightCm = height * 2.54;
}
var bmr;
if (genderMale) {
// Mifflin-St Jeor Equation for Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
// Mifflin-St Jeor Equation for Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
var tdee = bmr * activityLevelMultiplier;
var recommendedCalories = tdee;
var goalDescription = "";
switch (goal) {
case "maintain":
goalDescription = "to maintain your current weight";
break;
case "mildLoss":
recommendedCalories -= 250; // ~0.25 kg/week loss
goalDescription = "for mild weight loss (approx. 0.25 kg/week)";
break;
case "moderateLoss":
recommendedCalories -= 500; // ~0.5 kg/week loss
goalDescription = "for moderate weight loss (approx. 0.5 kg/week)";
break;
case "extremeLoss":
recommendedCalories -= 1000; // ~1 kg/week loss (use with caution)
goalDescription = "for extreme weight loss (approx. 1 kg/week – consult a professional)";
break;
case "mildGain":
recommendedCalories += 250; // ~0.25 kg/week gain
goalDescription = "for mild weight gain (approx. 0.25 kg/week)";
break;
case "moderateGain":
recommendedCalories += 500; // ~0.5 kg/week gain
goalDescription = "for moderate weight gain (approx. 0.5 kg/week)";
break;
case "extremeGain":
recommendedCalories += 1000; // ~1 kg/week gain (use with caution)
goalDescription = "for extreme weight gain (approx. 1 kg/week – consult a professional)";
break;
}
// Ensure calories don't go too low for safety, especially for extreme loss
if (recommendedCalories < 1200 && (goal === "extremeLoss" || goal === "moderateLoss")) {
resultDiv.innerHTML = "Calculated calories are very low (" + Math.round(recommendedCalories) + " kcal). Please consult a healthcare professional before attempting such a low-calorie diet.";
return;
}
resultDiv.innerHTML =
"Your estimated Basal Metabolic Rate (BMR):
" + Math.round(bmr) + " calories/day" +
"Your estimated Total Daily Energy Expenditure (TDEE):
" + Math.round(tdee) + " calories/day" +
"Based on your goal " + goalDescription + ", your recommended daily calorie intake is approximately:
" + Math.round(recommendedCalories) + " calories";
}