Heart Rate Fat Burn Zone Calculator

Heart Rate Fat Burn Zone Calculator

Optimize your workouts by finding the perfect intensity to maximize fat oxidation.

Your Target Fat Burn Results:

Estimated Max Heart Rate: BPM

Zone Intensity: 60% – 70% of Heart Rate Reserve

What is the Fat Burn Zone?

The "Fat Burn Zone" is a specific heart rate range where your body primarily uses stored body fat as its main fuel source rather than carbohydrates. While you burn more total calories at higher intensities, the percentage of calories derived from fat is highest when your heart rate is between 60% and 70% of its maximum capacity.

The Karvonen Formula Explained

This calculator uses the Karvonen Formula, which is more accurate than simple age-based formulas because it accounts for your Resting Heart Rate (RHR). By calculating your Heart Rate Reserve (HRR), we can find a more personalized zone that reflects your current cardiovascular fitness level.

How to Use These Results

• Warm-up: Spend 5-10 minutes gradually bringing your heart rate up.
• Consistency: Aim to stay within your calculated BPM range for at least 30-45 minutes.
• The "Talk Test": In this zone, you should be able to speak in short sentences but still be breathing deeply.

Example Calculation:
A 35-year-old with a resting heart rate of 70 BPM:
1. Max HR: 220 – 35 = 185 BPM
2. Heart Rate Reserve: 185 – 70 = 115 BPM
3. Lower Bound (60%): (115 × 0.60) + 70 = 139 BPM
4. Upper Bound (70%): (115 × 0.70) + 70 = 151 BPM

function calculateFatBurnZone() { var age = document.getElementById("hr_age").value; var rhr = document.getElementById("hr_resting").value; var resultsDiv = document.getElementById("hr_results"); var rangeDisplay = document.getElementById("zone_range"); var maxDisplay = document.getElementById("max_hr_val"); if (age === "" || rhr === "" || age <= 0 || rhr <= 0) { alert("Please enter valid positive numbers for Age and Resting Heart Rate."); return; } var ageNum = parseFloat(age); var rhrNum = parseFloat(rhr); // Formula: Karvonen // Max HR = 220 – Age var maxHr = 220 – ageNum; // Heart Rate Reserve = Max HR – Resting HR var hrr = maxHr – rhrNum; if (hrr <= 0) { alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs."); return; } // Fat burn zone is 60% to 70% intensity var lowerLimit = Math.round((hrr * 0.60) + rhrNum); var upperLimit = Math.round((hrr * 0.70) + rhrNum); rangeDisplay.innerHTML = lowerLimit + " – " + upperLimit + " BPM"; maxDisplay.innerHTML = maxHr; resultsDiv.style.display = "block"; // Smooth scroll to result resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }