Leave blank for standard formula, fill for Karvonen method (more accurate).
Maximum Heart Rate (MHR):–
Fat Burning Zone (60-70%):–
Calculation Method:–
function calculateFatBurn() {
var ageInput = document.getElementById('fbhr_age').value;
var rhrInput = document.getElementById('fbhr_rhr').value;
var resultBox = document.getElementById('fbhr_result');
// Convert inputs
var age = parseFloat(ageInput);
var rhr = parseFloat(rhrInput);
// Validation
if (isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
var maxHeartRate = 220 – age;
var lowerBound = 0;
var upperBound = 0;
var methodText = "";
// Check if RHR is provided for Karvonen method
if (!isNaN(rhr) && rhr > 0) {
// Karvonen Formula: Target Heart Rate = ((max HR − resting HR) × %Intensity) + resting HR
var heartRateReserve = maxHeartRate – rhr;
// Fat burn is typically 60% to 70%
lowerBound = (heartRateReserve * 0.60) + rhr;
upperBound = (heartRateReserve * 0.70) + rhr;
methodText = "Karvonen Formula (Personalized)";
} else {
// Standard Formula: Target Heart Rate = max HR * %Intensity
lowerBound = maxHeartRate * 0.60;
upperBound = maxHeartRate * 0.70;
methodText = "Standard Percentage (MHR)";
}
// Update DOM
document.getElementById('display_mhr').innerHTML = Math.round(maxHeartRate) + " bpm";
document.getElementById('display_zone').innerHTML = Math.round(lowerBound) + " – " + Math.round(upperBound) + " bpm";
document.getElementById('display_method').innerHTML = methodText;
// Show results
resultBox.style.display = 'block';
}
Understanding Your Fat Burning Heart Rate
Finding the optimal heart rate for burning fat is a key component of a successful weight loss or endurance training program. The "Fat Burning Zone" refers to a specific intensity level where your body relies primarily on stored fat as its fuel source, rather than carbohydrates (glycogen).
What is the Fat Burning Zone?
Physiologically, the fat burning zone occurs when you exercise at a moderate intensity, typically between 60% and 70% of your Maximum Heart Rate (MHR). At this intensity, your body has enough oxygen available to oxidize fat efficiently for energy.
Low Intensity (50-60%): Good for warm-ups and recovery. Burns fat but fewer total calories.
Fat Burning Zone (60-70%): The "sweet spot" where the percentage of calories burned from fat is highest.
Aerobic Zone (70-80%): Improves cardiovascular fitness. You burn more total calories, but a lower percentage comes from fat.
How We Calculate Your Zone
This calculator employs two different methods depending on the data you provide:
1. The Standard Method (MHR)
If you only enter your age, we use the standard Maximum Heart Rate formula (220 – Age). We then calculate 60% and 70% of this number. This provides a good general baseline for most people.
2. The Karvonen Formula (Recommended)
If you input your Resting Heart Rate (RHR), the calculator switches to the Karvonen formula. This is significantly more accurate because it accounts for your current fitness level. A lower resting heart rate usually indicates better cardiovascular health.
To get the most accurate result from this tool, measure your pulse immediately after waking up in the morning, before you get out of bed. Count the beats for 60 seconds. Repeat this for 3 days and take the average.
Disclaimer: This calculator is for informational purposes only. Always consult with a healthcare professional or physician before starting a new exercise routine, especially if you have pre-existing health conditions.