Optional: Enter for Karvonen Formula accuracy. Leave blank for Standard Formula.
Your Heart Rate Profile
Estimated Max Heart Rate:— bpm
Calculation Method:—
Your Fat Burning Zone (60-70%)
110 – 130 BPM
Target this range for 30-60 minutes for optimal fat oxidation.
function calculateFatBurn() {
// Get input values
var ageInput = document.getElementById('fb_age').value;
var rhrInput = document.getElementById('fb_rhr').value;
var resultDiv = document.getElementById('fb_result');
// Basic validation
if (!ageInput || ageInput 120) {
alert("Please enter a valid age between 10 and 120.");
return;
}
var age = parseFloat(ageInput);
var mhr = 220 – age; // Standard max heart rate formula
var lowZone, highZone, methodText;
// Logic branching: Standard vs Karvonen
if (rhrInput && rhrInput > 30 && rhrInput < 200) {
// Karvonen Formula: TargetHR = ((maxHR − restingHR) × %Intensity) + restingHR
var rhr = parseFloat(rhrInput);
var hrr = mhr – rhr; // Heart Rate Reserve
lowZone = Math.round((hrr * 0.60) + rhr);
highZone = Math.round((hrr * 0.70) + rhr);
methodText = "Karvonen (Most Accurate)";
} else {
// Standard Formula: TargetHR = maxHR * %Intensity
lowZone = Math.round(mhr * 0.60);
highZone = Math.round(mhr * 0.70);
methodText = "Standard (Age-based)";
}
// Display Results
document.getElementById('res_mhr').innerHTML = mhr + " bpm";
document.getElementById('res_method').innerHTML = methodText;
document.getElementById('res_zone').innerHTML = lowZone + " – " + highZone + " BPM";
resultDiv.style.display = "block";
}
Understanding Your Fat Burning Heart Rate
Finding the optimal intensity for weight loss is key to maximizing the efficiency of your workouts. This Fat Burn Heart Rate Calculator Free tool helps you identify the specific heart rate zone where your body burns the highest percentage of calories from fat stores rather than carbohydrates.
What is the "Fat Burn Zone"?
The "Fat Burn Zone" is generally defined as an aerobic exercise intensity between 60% and 70% of your maximum heart rate. At this moderate intensity, the body has sufficient oxygen available to oxidize fat for fuel. While higher intensity workouts (like HIIT) burn more calories overall per minute, the percentage of energy derived from fat is highest in this lower, steady-state zone.
The Difference Between Standard and Karvonen Formulas
Our calculator offers two methods of calculation depending on the data you provide:
Standard Method (MHR): This calculates your zones based solely on your age (220 – Age). It provides a general baseline suitable for beginners.
Karvonen Method (HRR): This advanced formula incorporates your Resting Heart Rate (RHR). By accounting for your cardiovascular fitness level (via RHR), it provides a much more personalized and accurate target zone. We recommend measuring your pulse first thing in the morning to use this feature.
Heart Rate Zones Reference Chart
Zone
Intensity (%)
Primary Benefit
Warm Up
50-60%
Recovery, circulation, warm-up
Fat Burn
60-70%
Maximal fat oxidation, endurance base
Aerobic
70-80%
Cardiovascular fitness, aerobic capacity
Anaerobic
80-90%
Lactic acid tolerance, high speed
VO2 Max
90-100%
Maximum performance, sprinting
How to Use These Results
Once you have calculated your range (e.g., 115 – 135 BPM), aim to keep your heart rate within these numbers during steady-state cardio sessions such as brisk walking, light jogging, cycling, or swimming. For best results, consistency is key; aim for 30 to 60 minutes in this zone, 3 to 4 times per week.