body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
}
.calculator-wrapper {
background: #fdfdfd;
border: 1px solid #e0e0e0;
border-radius: 12px;
padding: 30px;
box-shadow: 0 4px 15px rgba(0,0,0,0.05);
margin-bottom: 40px;
}
.calculator-header {
text-align: center;
margin-bottom: 25px;
}
.calculator-header h2 {
margin: 0;
color: #2c3e50;
font-size: 24px;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #555;
}
.input-group input {
width: 100%;
padding: 12px;
border: 2px solid #ddd;
border-radius: 8px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.input-group input:focus {
border-color: #e74c3c;
outline: none;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #e74c3c;
color: white;
border: none;
border-radius: 8px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
}
.calc-btn:hover {
background-color: #c0392b;
}
#result-container {
margin-top: 30px;
padding: 20px;
background-color: #fcebeb;
border-radius: 8px;
display: none;
text-align: center;
}
.result-box {
margin: 10px 0;
}
.result-label {
font-size: 14px;
color: #666;
text-transform: uppercase;
letter-spacing: 1px;
}
.result-value {
font-size: 36px;
font-weight: 800;
color: #e74c3c;
}
.result-sub {
font-size: 18px;
color: #444;
margin-top: 5px;
}
.content-section {
margin-top: 40px;
}
.content-section h2 {
color: #2c3e50;
border-bottom: 2px solid #e74c3c;
padding-bottom: 10px;
margin-top: 30px;
}
.content-section p {
margin-bottom: 15px;
}
.content-section ul {
margin-bottom: 20px;
padding-left: 20px;
}
.content-section li {
margin-bottom: 10px;
}
.info-box {
background-color: #ecf0f1;
padding: 15px;
border-left: 5px solid #3498db;
margin: 20px 0;
}
@media (max-width: 600px) {
.calculator-wrapper {
padding: 20px;
}
}
function calculateFatBurn() {
// Get input values
var ageInput = document.getElementById('userAge');
var rhrInput = document.getElementById('restingHR');
var age = parseFloat(ageInput.value);
var rhr = parseFloat(rhrInput.value);
var resultDiv = document.getElementById('result-container');
// Validation
if (isNaN(age) || age 110) {
alert("Please enter a valid age between 10 and 110.");
return;
}
if (isNaN(rhr) || rhr 200) {
alert("Please enter a valid resting heart rate (usually between 40 and 100).");
return;
}
// 1. Calculate Maximum Heart Rate (MHR) using Standard Formula
var maxHR = 220 – age;
// 2. Calculate Heart Rate Reserve (HRR) – Karvonen Method
var hrr = maxHR – rhr;
// 3. Calculate Target Zones (60% to 70% intensity)
// Formula: (HRR * Intensity) + Resting Heart Rate
var minIntensity = 0.60;
var maxIntensity = 0.70;
var lowerZone = Math.round((hrr * minIntensity) + rhr);
var upperZone = Math.round((hrr * maxIntensity) + rhr);
// Display Results
document.getElementById('targetZoneDisplay').innerText = lowerZone + " – " + upperZone + " bpm";
document.getElementById('maxHRDisplay').innerText = maxHR + " bpm";
document.getElementById('hrrDisplay').innerText = hrr + " bpm";
resultDiv.style.display = 'block';
}
Understanding Your Fat Burning Zone
The "Fat Burning Zone" refers to a specific heart rate range where your body prioritizes fat stores as its primary source of energy during exercise. While high-intensity cardio burns more calories overall, working out at a moderate intensity (roughly 60% to 70% of your heart rate reserve) encourages the body to oxidize fat more efficiently.
This calculator uses the Karvonen Formula, which is widely considered more accurate than standard charts because it takes your Resting Heart Rate (RHR) into account. By factoring in your RHR, the results are tailored to your specific fitness level rather than just your age.
How the Calculation Works
To find your optimal heart rate for burning fat, we perform the following steps:
- Maximum Heart Rate (MHR): Estimated as 220 minus your age.
- Heart Rate Reserve (HRR): Your MHR minus your Resting Heart Rate. This represents the range of heart speeds available to you during exercise.
- Target Zone: We calculate 60% and 70% of your HRR and add your Resting Heart Rate back to these figures to find your specific training zone.
Why Resting Heart Rate Matters: A lower resting heart rate usually indicates better cardiovascular fitness. As you get fitter, your RHR will drop, and your fat burning zone will actually adjust. It is recommended to re-calculate your zone every few months as your fitness improves.
Tips for Training in the Zone
Once you have your numbers (e.g., 125 – 140 bpm), the goal is to keep your heart rate within this window for the duration of your workout.
- Duration is Key: Because the intensity is moderate, you should aim for longer sessions. 30 to 60 minutes is ideal for mobilizing fat stores.
- Consistency: Aim for 3 to 5 sessions per week. Walking on an incline, light jogging, cycling, or using an elliptical are excellent exercises to maintain a steady heart rate.
- Monitor Your Pulse: Use a smartwatch, fitness tracker, or the machine's hand sensors to check your pulse periodically to ensure you aren't dropping below or spiking above your target zone.
- The "Talk Test": If you don't have a monitor, use the talk test. In the fat burning zone, you should be breathing heavier than normal but still able to carry on a conversation without gasping for air.
Frequently Asked Questions
Is the fat burning zone the only way to lose weight?
No. Weight loss is primarily driven by a caloric deficit (burning more calories than you consume). However, training in the fat burning zone is often sustainable, less stressful on joints, and ensures a higher percentage of calories burned come from fat rather than glycogen (carbohydrates) or muscle tissue.
When is the best time to do this cardio?
Many experts suggest "fasted cardio" (first thing in the morning before eating) may slightly increase fat oxidation because insulin levels are low, but the most important factor is consistency. The best time is whenever you can stick to your routine.
What if my heart rate goes above the zone?
If you go above the upper limit (70%), you enter the "Cardio" or "Aerobic" zone. You will burn more total calories per minute, but the percentage of fat used for fuel decreases while the percentage of carbohydrates increases. This is excellent for cardiovascular endurance but can be harder to sustain for long periods compared to the fat burning zone.