Measure your pulse for 60 seconds while sitting quietly.
Your Target Fat Burning Zone:
(60% to 70% of your heart rate reserve + resting HR)
Understanding the Fat Burning Heart Rate Zone
The "fat-burning zone" is a specific heart rate range where your body primarily utilizes stored body fat for energy rather than carbohydrates. This zone typically occurs at 60% to 70% of your maximum heart rate. While high-intensity workouts burn more total calories, exercising within this zone allows for longer durations and ensures a higher percentage of calories burned come directly from fat stores.
How This Calculation Works
This calculator utilizes the Karvonen Formula, which is considered more accurate than the standard "220 minus age" method because it takes your individual fitness level (Resting Heart Rate) into account. The math follows these steps:
Imagine a 40-year-old individual with a resting heart rate of 70 BPM:
Max HR: 220 – 40 = 180 BPM
Heart Rate Reserve: 180 – 70 = 110 BPM
60% Intensity: (110 * 0.6) + 70 = 136 BPM
70% Intensity: (110 * 0.7) + 70 = 147 BPM
For this individual, keeping their pulse between 136 and 147 beats per minute would be the optimal window for fat oxidation.
Tips for Optimizing Your Workouts
To maximize your results using the fat-burning heart rate calculator, consider these strategies:
Consistency Over Intensity: Staying in this zone for 45-60 minutes is more effective for fat loss than a 10-minute sprint.
Monitor Your Progress: Use a chest strap or a reliable smartwatch to ensure you don't drift into higher intensity zones where your body switches to glucose burning.
Morning Cardio: Some studies suggest that performing cardio in the fat-burning zone on an empty stomach (fasted cardio) may further enhance fat utilization.
Combine with Strength Training: While the fat-burning zone is great for cardio, building muscle increases your basal metabolic rate, helping you burn more fat even at rest.
function calculateFatBurnZone() {
var age = parseFloat(document.getElementById("userAge").value);
var rhr = parseFloat(document.getElementById("restHR").value);
var resultDiv = document.getElementById("fbcResult");
var rangeDisplay = document.getElementById("hrRange");
var maxDisplay = document.getElementById("maxHRDisplay");
if (isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
if (isNaN(rhr) || rhr 150) {
alert("Please enter a valid resting heart rate (typical range is 40-100).");
return;
}
// Fox Formula for Max HR
var mhr = 220 – age;
// Heart Rate Reserve
var hrr = mhr – rhr;
if (hrr <= 0) {
alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs.");
return;
}
// Karvonen Calculation
var lowEnd = Math.round((hrr * 0.60) + rhr);
var highEnd = Math.round((hrr * 0.70) + rhr);
// Displaying Results
rangeDisplay.innerHTML = lowEnd + " – " + highEnd + " BPM";
maxDisplay.innerHTML = "Estimated Max Heart Rate: " + mhr + " BPMHeart Rate Reserve: " + hrr + " BPM";
resultDiv.style.display = "block";
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}