Calorie Deficit Calculator for Weight Loss
Use this calculator to estimate your daily calorie needs to achieve your weight loss goals. It calculates your Basal Metabolic Rate (BMR), Total Daily Energy Expenditure (TDEE), and then suggests a daily calorie intake to create a deficit for weight loss.
Understanding Calorie Deficit for Weight Loss
Weight loss fundamentally comes down to creating a calorie deficit. This means consuming fewer calories than your body burns over a period of time. When your body doesn't get enough energy from food, it starts to use stored energy, primarily from fat reserves, leading to weight loss.
How Your Body Burns Calories
Your body burns calories in three main ways:
- Basal Metabolic Rate (BMR): This is the number of calories your body burns at rest to maintain basic bodily functions like breathing, circulation, and cell production. It accounts for the largest portion of your daily calorie expenditure.
- Thermic Effect of Food (TEF): This is the energy your body uses to digest, absorb, and metabolize the food you eat. It's a smaller component, typically around 10% of your total calorie intake.
- Activity Energy Expenditure (AEE): This includes all calories burned through physical activity, from structured exercise to non-exercise activity thermogenesis (NEAT) like walking, fidgeting, and standing.
The sum of BMR, TEF, and AEE gives you your Total Daily Energy Expenditure (TDEE), which is the total number of calories your body burns in a day.
Calculating Your Calorie Needs
Our calculator uses the following steps to determine your calorie needs for weight loss:
- BMR Calculation: We use the Mifflin-St Jeor equation, which is widely recognized for its accuracy:
- 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
- TDEE Calculation: Your BMR is then multiplied by an activity factor to estimate your TDEE:
- Sedentary: BMR × 1.2 (little to no exercise)
- Lightly Active: BMR × 1.375 (light exercise/sports 1-3 days/week)
- Moderately Active: BMR × 1.55 (moderate exercise/sports 3-5 days/week)
- Very Active: BMR × 1.725 (hard exercise/sports 6-7 days a week)
- Extremely Active: BMR × 1.9 (very hard exercise/physical job)
- Calorie Deficit for Weight Loss: To lose weight, you need to consume fewer calories than your TDEE. A common guideline is that 1 kilogram of body fat is roughly equivalent to 7,700 calories. Therefore, to lose 0.5 kg (1.1 lbs) per week, you need a daily deficit of approximately 550 calories (7700 / 7 days). The calculator determines the necessary daily deficit based on your target weekly weight loss.
- Target Daily Calorie Intake: This is calculated by subtracting the required daily deficit from your TDEE.
Realistic Weight Loss Goals
A healthy and sustainable rate of weight loss is generally considered to be 0.5 to 1 kg (1 to 2 pounds) per week. Aiming for a larger deficit might lead to faster initial weight loss but can be difficult to sustain, potentially leading to nutrient deficiencies, muscle loss, and rebound weight gain. Always prioritize a balanced diet and regular physical activity.
Important Considerations
- Individual Variation: These calculations are estimates. Individual metabolic rates can vary due to genetics, hormones, and other factors.
- Nutrient Density: Focus on consuming nutrient-dense foods (lean proteins, whole grains, fruits, vegetables) within your calorie target to ensure you're getting essential vitamins and minerals.
- Hydration: Drink plenty of water throughout the day.
- Exercise: While diet is crucial for weight loss, incorporating regular physical activity can help increase your TDEE, improve body composition, and offer numerous health benefits.
- Consult a Professional: Before making significant changes to your diet or exercise routine, especially if you have underlying health conditions, it's always best to consult with a doctor or a registered dietitian.
This calculator provides a starting point. Listen to your body, adjust your intake as needed, and focus on building sustainable healthy habits.
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function calculateCalorieDeficit() {
var age = parseFloat(document.getElementById("age").value);
var gender = document.querySelector('input[name="gender"]:checked').value;
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var activityLevel = document.getElementById("activityLevel").value;
var targetWeightLossKg = parseFloat(document.getElementById("targetWeightLossKg").value);
var resultDiv = document.getElementById("result");
// Input validation
if (isNaN(age) || age <= 0 ||
isNaN(weightKg) || weightKg <= 0 ||
isNaN(heightCm) || heightCm <= 0 ||
isNaN(targetWeightLossKg) || targetWeightLossKg <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
var bmr;
// Mifflin-St Jeor Equation
if (gender === "male") {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else { // female
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
var activityFactor;
switch (activityLevel) {
case "sedentary":
activityFactor = 1.2;
break;
case "lightlyActive":
activityFactor = 1.375;
break;
case "moderatelyActive":
activityFactor = 1.55;
break;
case "veryActive":
activityFactor = 1.725;
break;
case "extremelyActive":
activityFactor = 1.9;
break;
default:
activityFactor = 1.2; // Default to sedentary if somehow not selected
}
var tdee = bmr * activityFactor;
// 1 kg of fat is approximately 7700 calories
var dailyCalorieDeficitNeeded = (targetWeightLossKg * 7700) / 7;
var targetDailyCalories = tdee – dailyCalorieDeficitNeeded;
if (targetDailyCalories < 1200 && gender === "female") {
resultDiv.innerHTML = "
Warning: The calculated target daily calorie intake of " + Math.round(targetDailyCalories) + " calories is very low for a female. Consuming less than 1200 calories per day is generally not recommended without medical supervision.";
} else if (targetDailyCalories < 1500 && gender === "male") {
resultDiv.innerHTML = "
Warning: The calculated target daily calorie intake of " + Math.round(targetDailyCalories) + " calories is very low for a male. Consuming less than 1500 calories per day is generally not recommended without medical supervision.";
} else if (targetDailyCalories <= 0) {
resultDiv.innerHTML = "The calculated target daily calorie intake is too low or negative. Please review your inputs, especially the target weight loss.";
} else {
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" +
"To lose
" + targetWeightLossKg + " kg per week, you need a daily calorie deficit of approximately
" + Math.round(dailyCalorieDeficitNeeded) + " calories/day." +
"Your target daily calorie intake for weight loss:
" + Math.round(targetDailyCalories) + " calories/day" +
"
Remember, these are estimates. Consult a healthcare professional for personalized advice.";
}
}