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, physical job)
Lose Weight (approx. 1 lb/week)
Slight Weight Loss (approx. 0.5 lb/week)
Maintain Weight
Slight Weight Gain (approx. 0.5 lb/week)
Gain Weight (approx. 1 lb/week)
Male
Female
Understanding Your Calorie and Macro Needs
Calculating your daily calorie and macronutrient (macros) needs is a fundamental step towards achieving your health and fitness goals, whether it's weight loss, muscle gain, or simply maintaining your current physique. This calculator provides an estimate based on established formulas, taking into account your personal characteristics and lifestyle.
Basal Metabolic Rate (BMR)
The calculation begins with estimating your Basal Metabolic Rate (BMR). This is the minimum number of calories your body needs to perform basic life-sustaining functions like breathing, circulating blood, and maintaining body temperature, all at rest. We use the Mifflin-St Jeor Equation, which is widely considered one of the most accurate BMR estimation 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)
Your BMR represents your calorie needs at rest. However, you expend more calories throughout the day due to physical activity. Your Total Daily Energy Expenditure (TDEE) accounts for this by multiplying your BMR by an activity factor:
TDEE = BMR × Activity Level Factor
The activity factors provided in the calculator represent typical daily energy expenditure based on exercise frequency and intensity.
Calorie Target for Goal
To achieve a specific weight goal (gain, lose, or maintain), your TDEE is adjusted. A deficit of approximately 3500 calories equates to about one pound of fat loss, while a surplus of the same amount leads to about one pound of weight gain. The calculator applies a daily calorie adjustment based on your selected goal:
A 500 calorie deficit per day aims for roughly 1 lb of weight loss per week.
A 250 calorie deficit per day aims for roughly 0.5 lb of weight loss per week.
A 250 calorie surplus per day aims for roughly 0.5 lb of weight gain per week.
A 500 calorie surplus per day aims for roughly 1 lb of weight gain per week.
Your "Target Daily Calories" is your TDEE plus or minus the daily adjustment for your goal.
Macronutrient Distribution
Macronutrients are the nutrients your body needs in large amounts: carbohydrates, protein, and fats. Distributing these appropriately is crucial for health, energy, and body composition. The calculator provides a common distribution target:
Protein: Typically set at 1.6-2.2 grams per kilogram of body weight. Protein is essential for muscle repair and growth, and satiety.
Fat: Typically set at 20-30% of total daily calories. Healthy fats are vital for hormone production and nutrient absorption.
Carbohydrates: The remaining calories are allocated to carbohydrates, which are the body's primary energy source.
The calculator uses a standard macro split that prioritizes sufficient protein and healthy fats, with the remainder from carbohydrates. These are then converted into grams based on their caloric value:
1 gram of Protein = 4 calories
1 gram of Carbohydrate = 4 calories
1 gram of Fat = 9 calories
Important Considerations
This calculator provides estimates. Individual metabolism, body composition, and the thermic effect of food can vary. It's always recommended to consult with a healthcare professional or a registered dietitian for personalized advice, especially if you have specific health conditions or dietary requirements. Monitor your progress and adjust your intake as needed.
function calculateMacros() {
var age = parseFloat(document.getElementById("age").value);
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var gender = document.getElementById("gender").value;
var activityLevel = parseFloat(document.getElementById("activityLevel").value);
var goal = parseFloat(document.getElementById("goal").value);
var errorMessages = [];
if (isNaN(age) || age <= 0) errorMessages.push("Please enter a valid age.");
if (isNaN(weightKg) || weightKg <= 0) errorMessages.push("Please enter a valid weight in kg.");
if (isNaN(heightCm) || heightCm 0) {
document.getElementById("result").innerHTML = "Error: " + errorMessages.join(" ");
return;
}
var bmr = 0;
if (gender === "male") {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else { // female
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
var tdee = bmr * activityLevel;
var targetCalories = tdee + goal;
// Ensure target calories don't go below a very low minimum for safety
if (targetCalories < 1200) {
targetCalories = 1200; // Minimum safe calorie intake
}
// Macro calculations (common split: ~40% carbs, 30% protein, 30% fat or protein at 1.6-2.2g/kg)
// Let's prioritize protein and fat and fill the rest with carbs for simplicity.
var proteinGrams = weightKg * 1.8; // Aiming for 1.8g/kg which is within the recommended range
var proteinCalories = proteinGrams * 4;
// Allocate 30% of total calories to fat
var fatCalories = targetCalories * 0.30;
var fatGrams = fatCalories / 9;
// Calculate remaining calories for carbs
var carbCalories = targetCalories – proteinCalories – fatCalories;
var carbGrams = carbCalories / 4;
// Adjust carb grams if they become negative or too low due to high protein/fat targets
if (carbGrams < 0) {
// This scenario means protein + fat calories exceed total target calories.
// This can happen with very aggressive goals or specific macro preferences.
// For a general calculator, we might need to adjust the initial percentages or cap them.
// For this example, we'll assume a balanced distribution and alert if issues arise.
// A more complex calculator might dynamically adjust protein/fat percentages.
// For simplicity here, we'll slightly reduce protein if carbGrams is negative,
// but ideally, this would involve re-evaluating the split.
console.warn("Carbohydrate calculation resulted in negative grams. Adjusting macro split may be needed.");
// Let's recalculate assuming a minimum of 20% fat and ensure protein doesn't push it over.
fatCalories = targetCalories * 0.25; // Reduce fat percentage slightly
fatGrams = fatCalories / 9;
carbCalories = targetCalories – proteinCalories – fatCalories;
carbGrams = carbCalories / 4;
if (carbGrams < 0) { // If still negative, cap protein or signal issue
carbGrams = 0; // Or a very small minimum like 50g
proteinCalories = targetCalories – proteinCalories – fatCalories; // Recalculate protein based on remaining
proteinGrams = proteinCalories / 4;
}
}
var resultHtml = 'Your Estimated Daily Needs:' +
targetCalories.toFixed(0) + ' Calories' +
'Macronutrient Breakdown:' +
'Protein: ' + proteinGrams.toFixed(0) + 'g' +
'Fat: ' + fatGrams.toFixed(0) + 'g' +
'Carbohydrates: ' + carbGrams.toFixed(0) + 'g';
document.getElementById("result").innerHTML = resultHtml;
}