Sedentary (Office job, little exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Exercise 6-7 days/week)
Extra Active (Physical job + training)
Maintain Current Weight
Fat Loss (Deficit)
Muscle Gain (Surplus)
Your Daily Calorie Target
0
Calories per day
Recommended Macros
0g
Protein
0g
Fats
0g
Carbs
Mastering Your Metabolism with CalZilla
Understanding the energy balance of your body is the fundamental pillar of any fitness transformation. Whether you are looking to shed body fat, build lean muscle, or maintain your current physique, the CalZilla calculator utilizes the Mifflin-St Jeor equation—considered the gold standard in metabolic estimation—to provide you with accurate daily targets.
What is TDEE?
Your Total Daily Energy Expenditure (TDEE) is the cumulative number of calories you burn in 24 hours. It is composed of three main factors:
Basal Metabolic Rate (BMR): The energy required to keep your body functioning at rest (breathing, blood circulation, cell repair).
Physical Activity Level: Calories burned during exercise and daily movement.
Thermic Effect of Food (TEF): Energy used to digest and process the nutrients you eat.
Understanding Your Results
The CalZilla calculator breaks down your results into two critical components: Energy and Macros.
1. Calorie Target
This is your primary "budget" for the day. If your goal is Fat Loss, the calculator subtracts approximately 20% (usually ~500 calories) from your TDEE to create a sustainable deficit. For Muscle Gain, it adds a surplus to fuel hypertrophy. For Maintenance, it matches your output exactly.
2. Macronutrients
Not all calories are created equal. The macro breakdown provided balances your intake for optimal performance:
Protein: Essential for muscle repair and satiety. High protein intake helps preserve lean mass during a diet.
Fats: Vital for hormonal health and nutrient absorption.
Carbohydrates: The body's preferred fuel source for high-intensity training and brain function.
How to Use These Numbers
Consistency is key. Track your intake using these targets for 2-3 weeks. Weigh yourself daily and take a weekly average. If your weight trend isn't moving in the desired direction, adjust your daily calories by +/- 100 to 200. Remember, a calculator provides a statistical estimate; your body provides the real data.
function calculateCalZilla() {
// 1. Get input values
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var weightLbs = parseFloat(document.getElementById('weight').value);
var heightFt = parseFloat(document.getElementById('height_ft').value);
var heightIn = parseFloat(document.getElementById('height_in').value);
var activityMultiplier = parseFloat(document.getElementById('activity').value);
var goal = document.getElementById('goal').value;
// 2. Validation
if (isNaN(age) || isNaN(weightLbs) || isNaN(heightFt) || isNaN(heightIn)) {
alert("Please enter valid numbers for Age, Weight, and Height.");
return;
}
// 3. Convert Units
// Weight: lbs to kg
var weightKg = weightLbs * 0.453592;
// Height: ft/in to cm
var totalInches = (heightFt * 12) + heightIn;
var heightCm = totalInches * 2.54;
// 4. Calculate BMR (Mifflin-St Jeor Equation)
var bmr = 0;
if (gender === 'male') {
// Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
// Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// 5. Calculate TDEE (Maintenance Calories)
var tdee = bmr * activityMultiplier;
// 6. Adjust for Goal
var targetCalories = tdee;
if (goal === 'cut') {
targetCalories = tdee – 500; // 500 cal deficit
} else if (goal === 'bulk') {
targetCalories = tdee + 300; // 300 cal surplus (lean bulk)
}
// Ensure calories don't drop dangerously low
if (targetCalories < 1200) targetCalories = 1200;
// 7. Calculate Macros
// Using a balanced split: 30% Protein, 35% Fat, 35% Carbs
// Protein = 4 cal/g, Fat = 9 cal/g, Carbs = 4 cal/g
var proteinCals = targetCalories * 0.30;
var fatCals = targetCalories * 0.35;
var carbCals = targetCalories * 0.35;
var proteinGrams = proteinCals / 4;
var fatGrams = fatCals / 9;
var carbGrams = carbCals / 4;
// 8. Display Results
document.getElementById('displayCalories').innerHTML = Math.round(targetCalories);
document.getElementById('displayProtein').innerHTML = Math.round(proteinGrams) + "g";
document.getElementById('displayFats').innerHTML = Math.round(fatGrams) + "g";
document.getElementById('displayCarbs').innerHTML = Math.round(carbGrams) + "g";
// Show result div
document.getElementById('results').style.display = 'block';
}