Heart Rate Fat-Burning Zone Calculator
Optimize your workout for maximum weight loss
Measure while sitting quietly for 1 min
Your Personalized Results:
Target this range for efficient fat oxidation during steady-state cardio.
Target this range to improve cardiovascular endurance and heart health.
Understanding Your Fat-Burning Zone
When you exercise, your body primarily uses two sources of fuel: fat and glycogen (carbohydrates). The intensity of your workout determines which fuel source is dominant. The “fat-burning zone” refers to a specific heart rate range where a higher percentage of calories burned comes from stored body fat rather than blood sugar or muscle glycogen.
How We Calculate Your Zones
This calculator uses the Karvonen Formula, which is more accurate than simple age-based formulas because it accounts for your Resting Heart Rate (RHR). This determines your “Heart Rate Reserve” (the difference between your max heart rate and your resting heart rate).
- Max Heart Rate (MHR): Estimated as 220 minus your age.
- Heart Rate Reserve (HRR): MHR minus Resting Heart Rate.
- The Calculation: (HRR × Intensity%) + Resting Heart Rate.
Example Calculation
If you are a 40-year-old with a resting heart rate of 60 BPM:
- Max Heart Rate: 220 – 40 = 180 BPM.
- Heart Rate Reserve: 180 – 60 = 120 BPM.
- Fat Burning (60%): (120 × 0.60) + 60 = 132 BPM.
- Fat Burning (70%): (120 × 0.70) + 60 = 144 BPM.
In this example, your target range for fat loss is 132 to 144 beats per minute.
Why Use This Calculator?
Exercising at too high an intensity (like sprinting) burns more total calories per minute, but relies heavily on carbohydrates. Exercising at too low an intensity may not burn enough total calories to see progress. The fat-burning zone provides a “sweet spot” for long-duration cardio sessions where you can sustain activity while maximizing fat metabolism.
Note: While this calculator provides a scientifically-backed estimate, individual physiology varies. Always consult with a healthcare professional before starting a new high-intensity exercise regimen.
function calculateFatZone() {
var age = parseFloat(document.getElementById(‘hrAge’).value);
var restingHR = parseFloat(document.getElementById(‘hrResting’).value);
var resultsDiv = document.getElementById(‘hrResults’);
var fatZoneSpan = document.getElementById(‘fatZoneRange’);
var cardioZoneSpan = document.getElementById(‘cardioZoneRange’);
var maxHRSpan = document.getElementById(‘maxHR’);
if (isNaN(age) || isNaN(restingHR) || age <= 0 || restingHR <= 0) {
alert("Please enter valid positive numbers for Age and Resting Heart Rate.");
return;
}
// Fox Formula for Max HR
var maxHR = 220 – age;
// Karvonen Formula: Target Heart Rate = ((Max HR − Resting HR) × %Intensity) + Resting HR
var hrReserve = maxHR – restingHR;
// Fat Burning Zone (60% to 70%)
var fatLower = Math.round((hrReserve * 0.60) + restingHR);
var fatUpper = Math.round((hrReserve * 0.70) + restingHR);
// Cardio Zone (70% to 80%)
var cardioLower = Math.round((hrReserve * 0.70) + restingHR);
var cardioUpper = Math.round((hrReserve * 0.80) + restingHR);
// Display values
maxHRSpan.innerText = maxHR;
fatZoneSpan.innerText = fatLower + " – " + fatUpper;
cardioZoneSpan.innerText = cardioLower + " – " + cardioUpper;
// Show results
resultsDiv.style.display = 'block';
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}