Calorie Deficit Calculator
.calculator-widget-container {
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background: #fff;
border: 1px solid #e0e0e0;
border-radius: 8px;
box-shadow: 0 4px 12px rgba(0,0,0,0.05);
}
.calc-header {
text-align: center;
margin-bottom: 25px;
}
.calc-header h2 {
margin: 0 0 10px 0;
color: #2c3e50;
}
.calc-header p {
color: #666;
font-size: 0.95em;
}
.calc-row {
display: flex;
flex-wrap: wrap;
margin-bottom: 15px;
gap: 15px;
}
.calc-col {
flex: 1;
min-width: 200px;
display: flex;
flex-direction: column;
}
.calc-col label {
font-weight: 600;
margin-bottom: 5px;
color: #34495e;
font-size: 0.9em;
}
.calc-input, .calc-select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
transition: border-color 0.3s;
}
.calc-input:focus, .calc-select:focus {
border-color: #3498db;
outline: none;
}
.radio-group {
display: flex;
gap: 20px;
padding: 10px 0;
}
.radio-group label {
font-weight: normal;
cursor: pointer;
display: flex;
align-items: center;
gap: 5px;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #e74c3c;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
margin-top: 10px;
transition: background-color 0.3s;
}
.calc-btn:hover {
background-color: #c0392b;
}
.result-box {
margin-top: 30px;
padding: 20px;
background-color: #f8f9fa;
border-left: 5px solid #e74c3c;
border-radius: 4px;
display: none; /* Hidden by default */
}
.result-row {
display: flex;
justify-content: space-between;
align-items: center;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
color: #555;
font-weight: 600;
}
.result-value {
font-size: 1.2em;
font-weight: bold;
color: #2c3e50;
}
.highlight-result {
color: #e74c3c;
font-size: 1.5em;
}
.article-content {
max-width: 800px;
margin: 40px auto;
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
}
.article-content h2 {
color: #2c3e50;
margin-top: 30px;
border-bottom: 2px solid #ecf0f1;
padding-bottom: 10px;
}
.article-content h3 {
color: #34495e;
margin-top: 25px;
}
.article-content ul {
margin-bottom: 20px;
padding-left: 20px;
}
.article-content li {
margin-bottom: 10px;
}
.info-box {
background: #e8f6f3;
padding: 15px;
border-radius: 5px;
border: 1px solid #d1f2eb;
margin: 20px 0;
}
@media (max-width: 600px) {
.calc-row {
flex-direction: column;
gap: 10px;
}
}
function calculateDeficit() {
// 1. Get Inputs
var age = parseFloat(document.getElementById('age').value);
var weightLbs = parseFloat(document.getElementById('weight_lbs').value);
var heightFt = parseFloat(document.getElementById('height_ft').value);
var heightIn = parseFloat(document.getElementById('height_in').value);
var activity = parseFloat(document.getElementById('activity_level').value);
var goal = parseFloat(document.getElementById('deficit_goal').value);
var genderMale = document.getElementById('gender_male').checked;
// 2. Validation
if (isNaN(age) || isNaN(weightLbs) || isNaN(heightFt) || isNaN(heightIn)) {
alert("Please enter valid numbers for age, weight, and height.");
return;
}
// 3. Conversion to Metric (Mifflin-St Jeor Formula requires Metric)
// 1 lb = 0.453592 kg
// 1 ft = 30.48 cm, 1 in = 2.54 cm
var weightKg = weightLbs * 0.453592;
var heightCm = (heightFt * 30.48) + (heightIn * 2.54);
// 4. Calculate BMR (Basal Metabolic Rate)
// Formula: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + S
// S is +5 for men, -161 for women
var bmr;
if (genderMale) {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// 5. Calculate TDEE (Total Daily Energy Expenditure)
var tdee = bmr * activity;
// 6. Calculate Deficit
// 1 lb of fat approx 3500 calories
// Daily deficit needed = (Goal Lbs * 3500) / 7
var dailyDeficit = (goal * 3500) / 7;
var targetCalories = tdee – dailyDeficit;
// Safety Check: Don't recommend dangerous levels
var warning = "";
var minLimit = genderMale ? 1500 : 1200;
// If target is too low, set it to minLimit (optional logic, but here we just show the calculation
// and var the user decide, but we won't show negative numbers).
if (targetCalories < minLimit) {
// Usually, this means the goal is too aggressive for the user's size
}
// 7. Update DOM
document.getElementById('res_tdee').innerHTML = Math.round(tdee) + " kcal";
document.getElementById('res_target').innerHTML = Math.round(targetCalories) + " kcal";
document.getElementById('res_bmr').innerHTML = Math.round(bmr);
document.getElementById('res_monthly_loss').innerHTML = (goal * 4.3).toFixed(1) + " lbs"; // 4.3 weeks in a month approx
document.getElementById('results').style.display = "block";
}
How to Calculate a Calorie Deficit for Weight Loss
Achieving weight loss ultimately comes down to the science of energy balance: Calories In versus Calories Out. A calorie deficit occurs when you consume fewer calories than your body burns in a day. This calculator uses the industry-standard Mifflin-St Jeor equation to estimate your needs accurately.
Understanding the Metrics
Before diving into your diet, it is crucial to understand the two main numbers this calculator provides:
- BMR (Basal Metabolic Rate): This is the number of calories your body needs just to perform basic life-sustaining functions like breathing and blood circulation while at complete rest. You should generally not eat below this number.
- TDEE (Total Daily Energy Expenditure): This is your BMR multiplied by your activity level. It represents the total energy you burn in a typical day, including work, exercise, and general movement.
Pro Tip: Your TDEE is your "Maintenance Calories." If you eat this amount, your weight will likely stay the same. To lose weight, you must eat below your TDEE.
How Big Should My Deficit Be?
While it might be tempting to slash calories drastically to see quick results, a moderate approach is more sustainable and preserves more muscle mass.
- Mild Deficit (250-300 kcal): Ideal for those who are already lean or want to prioritize athletic performance. Results will be slower (approx. 0.5 lbs/week).
- Moderate Deficit (500 kcal): The gold standard for weight loss. A 500-calorie daily deficit results in approximately 1 lb of fat loss per week (3,500 calorie rule).
- Aggressive Deficit (750-1000 kcal): Generally reserved for individuals with higher body fat percentages. It can result in 2 lbs of loss per week but requires strict adherence and monitoring.
Why Activity Level Matters
Many people underestimate or overestimate their activity level. Be honest with your input:
If you have an office job and go to the gym for 45 minutes three times a week, you are likely "Lightly Active" or "Moderately Active," not "Very Active." Overestimating activity can lead to a TDEE that is too high, meaning your "deficit" calories might actually be maintenance calories, stalling your progress.
Adjusting Over Time
As you lose weight, your body requires less energy to move. This means your BMR and TDEE will drop. It is recommended to recalculate your numbers after every 10-15 lbs of weight loss to ensure you remain in a deficit.