Sedentary (Office job, little exercise)
Light Activity (Exercise 1-3 days/week)
Moderate Activity (Exercise 3-5 days/week)
Very Active (Hard exercise 6-7 days/week)
Extra Active (Physical job + training)
Lose 0.5 lbs per week (Slow & Steady)
Lose 1 lb per week (Recommended)
Lose 1.5 lbs per week (Aggressive)
Lose 2 lbs per week (Very Aggressive)
Basal Metabolic Rate (BMR):0 kcal
Maintenance Calories (TDEE):0 kcal
Daily Calorie Deficit:0 kcal
Daily Target Calories to Reach Goal
0
Calories / Day
Warning: This target is very low. It is generally not recommended to go below 1200 (women) or 1500 (men) calories without medical supervision.
Understanding Your Calorie Deficit
Achieving weight loss is fundamentally a mathematical equation balanced by biology. To lose weight, you must consume fewer calories than your body burns, creating what is known as a calorie deficit. This calculator helps you determine exactly how much you need to eat to reach your weight loss goals safely and effectively.
How the Calculation Works
The logic behind this calculator relies on two primary metrics: your Basal Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE).
BMR (Basal Metabolic Rate): This is the number of calories your body needs to perform basic life-sustaining functions like breathing, circulation, and cell production while you are completely at rest. We use the Mifflin-St Jeor equation, widely considered the most accurate standard formula.
TDEE (Total Daily Energy Expenditure): Since you don't stay in bed all day, we multiply your BMR by an "activity factor" to determine how many total calories you burn in a day.
Setting a Safe Deficit
A standard pound of fat contains approximately 3,500 calories. Therefore, the math for weight loss breaks down as follows:
Lose 0.5 lbs/week: 250 calorie daily deficit.
Lose 1 lb/week: 500 calorie daily deficit.
Lose 2 lbs/week: 1,000 calorie daily deficit.
While it might be tempting to select the "Very Aggressive" option to lose weight quickly, research suggests that a deficit of 500 calories (1 lb per week) is the most sustainable. Extreme deficits can lead to muscle loss, nutritional deficiencies, and metabolic adaptation, where your body burns fewer calories in an attempt to conserve energy.
Factors That Affect Your Results
This calculator provides a scientific estimate, but individual results vary based on:
Muscle Mass: Muscle burns more calories than fat at rest. If you have a high muscle mass, your actual maintenance level might be higher than calculated.
NEAT (Non-Exercise Activity Thermogenesis): Fidgeting, walking to the car, and standing posture contribute significantly to daily burn and vary wildly between people.
Accuracy of Intake: Tracking calories accurately is difficult. Most people underestimate their food intake by 20-30%. Using a food scale and a tracking app is highly recommended alongside this calculator.
When to Recalculate
As you lose weight, your body requires less energy to move and function. A diet that worked when you were 200 lbs may be your maintenance calories when you reach 170 lbs. It is recommended to recalculate your numbers after every 10-15 lbs of weight loss to ensure you remain in a deficit.
function calculateDeficit() {
// 1. Get Input Values
var gender = document.getElementById('cd_gender').value;
var age = document.getElementById('cd_age').value;
var feet = document.getElementById('cd_feet').value;
var inches = document.getElementById('cd_inches').value;
var weightLbs = document.getElementById('cd_weight').value;
var activityMultiplier = parseFloat(document.getElementById('cd_activity').value);
var goalLbsPerWeek = parseFloat(document.getElementById('cd_goal').value);
// 2. Validation
if (age === "" || feet === "" || inches === "" || weightLbs === "") {
alert("Please fill in all fields to calculate your calories.");
return;
}
var ageNum = parseFloat(age);
var feetNum = parseFloat(feet);
var inchesNum = parseFloat(inches);
var weightNum = parseFloat(weightLbs);
if (isNaN(ageNum) || isNaN(feetNum) || isNaN(inchesNum) || isNaN(weightNum)) {
alert("Please enter valid numbers.");
return;
}
// 3. Conversions
// Height to cm: (Feet * 30.48) + (Inches * 2.54)
var heightCm = (feetNum * 30.48) + (inchesNum * 2.54);
// Weight to kg: Lbs / 2.20462
var weightKg = weightNum / 2.20462;
// 4. Calculate BMR (Mifflin-St Jeor Equation)
// Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
// Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
var bmr = 0;
if (gender === 'male') {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * ageNum) + 5;
} else {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * ageNum) – 161;
}
// 5. Calculate TDEE
var tdee = bmr * activityMultiplier;
// 6. Calculate Deficit
// 3500 calories = 1 lb of fat.
// Daily deficit needed = (Goal Lbs * 3500) / 7
var dailyDeficit = (goalLbsPerWeek * 3500) / 7;
// 7. Calculate Target Calories
var targetCalories = tdee – dailyDeficit;
// 8. Update UI
document.getElementById('res_bmr').innerHTML = Math.round(bmr).toLocaleString() + " kcal";
document.getElementById('res_tdee').innerHTML = Math.round(tdee).toLocaleString() + " kcal";
document.getElementById('res_deficit').innerHTML = "-" + Math.round(dailyDeficit) + " kcal";
document.getElementById('res_target').innerHTML = Math.round(targetCalories).toLocaleString();
// 9. Safety Check
// General rule: Men shouldn't go below 1500, Women below 1200 without medical supervision
var warningBox = document.getElementById('safety_warning');
var isUnsafe = false;
if (gender === 'male' && targetCalories < 1500) {
isUnsafe = true;
} else if (gender === 'female' && targetCalories < 1200) {
isUnsafe = true;
}
if (isUnsafe) {
warningBox.style.display = "block";
document.getElementById('res_target').style.color = "#d32f2f";
} else {
warningBox.style.display = "none";
document.getElementById('res_target').style.color = "#e74c3c";
}
// Show results container
document.getElementById('results').style.display = "block";
}