Calculate your personalized macronutrient targets based on your goals.
Sedentary (Little to no exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Exercise 6-7 days/week)
Extra Active (Very intense exercise daily, or physical job)
IIFYM stands for "If It Fits Your Macros." It's a flexible dieting approach that focuses on hitting specific daily targets for macronutrients (protein, carbohydrates, and fats) and total calories, rather than restricting certain foods. This allows for more dietary variety while still enabling individuals to achieve their fitness goals, whether it's fat loss, muscle gain, or maintenance.
How the IIFYM Macro Calculator Works:
This calculator estimates your daily caloric needs and then breaks them down into macronutrient targets. The process involves several steps:
Basal Metabolic Rate (BMR): This is the number of calories your body burns at rest to maintain basic functions. We use either the revised Harris-Benedict equation or the Mifflin-St Jeor equation, which are common and reliable formulas.
Mifflin-St Jeor (often considered more accurate):
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Harris-Benedict (Revised):
Men: BMR = (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years) + 88.362
Women: BMR = (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years) + 447.593
Total Daily Energy Expenditure (TDEE): This is your BMR multiplied by an activity factor. It represents the total calories you burn in a day, including all physical activity.
TDEE = BMR × Activity Factor
Calorie Goal: Based on your selected goal (lose weight, maintain, gain muscle), we adjust your TDEE. Losing weight typically involves a calorie deficit, while gaining muscle involves a surplus.
Target Calories = TDEE + Goal Adjustment (in kcal)
Macronutrient Breakdown:
Once your target calories are determined, the calculator uses your desired percentages for protein and fat to calculate the remaining percentage for carbohydrates.
Protein: 1 gram = 4 calories.
Carbohydrates: 1 gram = 4 calories.
Fat: 1 gram = 9 calories.
The calculator first determines the grams of protein and fat based on the percentage of total target calories, then calculates carbohydrates.
Important Note: These calculations provide estimates. Individual metabolic rates can vary. It's recommended to monitor your progress and adjust your macros as needed. Consulting with a registered dietitian or a certified nutritionist is always advisable for personalized guidance.
function calculateMacros() {
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var age = parseInt(document.getElementById("age").value);
var gender = document.getElementById("gender").value;
var activityLevel = parseFloat(document.getElementById("activityLevel").value);
var bmrMethod = document.getElementById("bmrMethod").value;
var goal = parseInt(document.getElementById("goal").value);
var proteinPercentage = parseFloat(document.getElementById("proteinPercentage").value);
var fatPercentage = parseFloat(document.getElementById("fatPercentage").value);
var resultContainer = document.getElementById("resultContainer");
var macroOutput = document.getElementById("macroOutput");
var calorieOutput = document.getElementById("calorieOutput");
// — Input Validation —
if (isNaN(weightKg) || weightKg <= 0 ||
isNaN(heightCm) || heightCm <= 0 ||
isNaN(age) || age <= 0 ||
isNaN(proteinPercentage) || proteinPercentage 100 ||
isNaN(fatPercentage) || fatPercentage 100) {
alert("Please enter valid positive numbers for weight, height, age, and percentages.");
resultContainer.style.display = 'none';
return;
}
// Ensure percentages don't exceed 100% when combined
if (proteinPercentage + fatPercentage >= 100) {
alert("Protein and Fat percentages combined cannot be 100% or more. Please adjust.");
resultContainer.style.display = 'none';
return;
}
var bmr = 0;
// — BMR Calculation —
if (bmrMethod === "mifflin-st-jeor") {
if (gender === "male") {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
} else { // harris-benedict
if (gender === "male") {
bmr = (13.397 * weightKg) + (4.799 * heightCm) – (5.677 * age) + 88.362;
} else {
bmr = (9.247 * weightKg) + (3.098 * heightCm) – (4.330 * age) + 447.593;
}
}
// — TDEE Calculation —
var tdee = bmr * activityLevel;
// — Target Calories Calculation —
var targetCalories = tdee + goal;
// — Macronutrient Calculation —
var proteinCalories = targetCalories * (proteinPercentage / 100);
var fatCalories = targetCalories * (fatPercentage / 100);
var carbCalories = targetCalories – proteinCalories – fatCalories;
var proteinGrams = proteinCalories / 4;
var fatGrams = fatCalories / 9;
var carbGrams = carbCalories / 4;
// — Display Results —
macroOutput.innerHTML =
proteinGrams.toFixed(0) + "g Protein" +
"" +
carbGrams.toFixed(0) + "g Carbohydrates" +
"" +
fatGrams.toFixed(0) + "g Fat";
calorieOutput.innerHTML = "Total Daily Calories: " + targetCalories.toFixed(0) + " kcal";
resultContainer.style.display = 'block';
}