Determine your optimal pulse zone to maximize fat oxidation.
Optional. Leave blank for standard formula.
Optimal Fat Burning Zone
— – — BPM
Maintain this heart rate for best results.
Maximum Heart Rate (MHR)
— BPM
Calculation Method Used
Standard
What is the Best Heart Rate to Burn Fat?
When engaging in cardiovascular exercise, your body uses two primary fuel sources: glycogen (stored sugar) and fat. The "Fat Burning Zone" typically occurs at an intensity of roughly 60% to 70% of your Maximum Heart Rate (MHR). In this zone, the body relies more heavily on fat for energy compared to higher intensity zones where glycogen becomes the dominant fuel source.
How This Calculator Works
This calculator utilizes two primary methods to determine your target heart rate:
Standard Formula: Calculates your Maximum Heart Rate as 220 – Age. The fat burning zone is simply 60-70% of this number. This is best if you do not know your resting heart rate.
Karvonen Formula: If you input your Resting Heart Rate (RHR), the calculator uses the Karvonen method. This is considered more accurate as it accounts for your specific fitness level by calculating your Heart Rate Reserve (HRR). The formula is: ((MHR – RHR) × Intensity) + RHR.
Why Target the Fat Burning Zone?
Exercising in this lower-intensity zone (often called Zone 2 training) allows you to sustain activity for longer durations. Since fat oxidation requires oxygen, lower intensities ensure your body gets enough oxygen to efficiently convert fat into energy. While High-Intensity Interval Training (HIIT) burns more calories overall per minute, the lower intensity zone is specifically efficient at teaching the body to mobilize fat stores.
Tips for Measuring Heart Rate
Wearables: Use a smart watch or chest strap for real-time monitoring.
Manual Check: Place two fingers on your radial artery (wrist) or carotid artery (neck), count the beats for 15 seconds, and multiply by 4.
Talk Test: In the fat burning zone, you should be able to hold a conversation without gasping for air.
function calculateFatBurnZone() {
// 1. Get input values
var ageInput = document.getElementById('fbh-age').value;
var rhrInput = document.getElementById('fbh-rhr').value;
var resultArea = document.getElementById('fbh-result-area');
// 2. Validate Age
if (ageInput === "" || isNaN(ageInput)) {
alert("Please enter a valid age.");
return;
}
var age = parseFloat(ageInput);
if (age 120) {
alert("Please enter a realistic age between 10 and 120.");
return;
}
// 3. Calculate Maximum Heart Rate (MHR) Standard Formula
var mhr = 220 – age;
// 4. Initialize variables for zone calculation
var minZone = 0;
var maxZone = 0;
var method = "";
var rhr = 0;
// 5. Determine Calculation Method (Standard vs Karvonen)
if (rhrInput !== "" && !isNaN(rhrInput)) {
rhr = parseFloat(rhrInput);
// Validate RHR
if (rhr 150) {
alert("Please enter a realistic resting heart rate (30-150 bpm) or leave it blank.");
return;
}
// KARVONEN FORMULA
// HRR = Heart Rate Reserve
var hrr = mhr – rhr;
// Fat Burn Zone is typically 60% to 70% intensity
minZone = (hrr * 0.60) + rhr;
maxZone = (hrr * 0.70) + rhr;
method = "Karvonen Formula (Personalized)";
} else {
// STANDARD FORMULA
// Fat Burn Zone is 60% to 70% of MHR
minZone = mhr * 0.60;
maxZone = mhr * 0.70;
method = "Standard Age-Based Formula";
}
// 6. Round results for display
minZone = Math.round(minZone);
maxZone = Math.round(maxZone);
mhr = Math.round(mhr);
// 7. Update the DOM
document.getElementById('fbh-display-zone').innerHTML = minZone + " – " + maxZone + " BPM";
document.getElementById('fbh-display-mhr').innerText = mhr + " BPM";
document.getElementById('fbh-display-method').innerText = method;
// 8. Show result container
resultArea.style.display = "block";
// 9. Scroll to results if on mobile
if(window.innerWidth < 600) {
resultArea.scrollIntoView({behavior: "smooth"});
}
}