Many fitness enthusiasts ask, "What heart rate should I maintain to lose weight?" The fat-burning zone is typically defined as exercising at an intensity where your body primarily uses stored fat for fuel rather than carbohydrates. This zone usually sits between 60% and 70% of your maximum heart rate.
How We Calculate Your Zones
This calculator uses two primary methodologies to determine your target heart rate:
The Fox Formula: The standard 220 minus your age is used to estimate your Maximum Heart Rate (MHR).
The Karvonen Formula: If you provide your resting heart rate, we use Heart Rate Reserve (HRR). This is often considered more accurate because it accounts for your individual fitness level.
Why the 60-70% Range?
At lower intensities (the fat-burning zone), a higher percentage of calories burned comes from fat. However, at higher intensities (70-85% of MHR), you burn more total calories. For weight loss, a combination of both is often most effective. Staying in the 60-70% zone is excellent for long-duration workouts, active recovery, and those just beginning their fitness journey.
Example Calculation for a 30-Year-Old
If you are 30 years old with a resting heart rate of 60 BPM:
Max Heart Rate: 220 – 30 = 190 BPM.
Heart Rate Reserve: 190 – 60 = 130 BPM.
Lower Bound (60%): (130 × 0.60) + 60 = 138 BPM.
Upper Bound (70%): (130 × 0.70) + 60 = 151 BPM.
In this example, your optimal fat-burning zone is between 138 and 151 beats per minute.
Pro Tip: To find your resting heart rate, measure your pulse for 60 seconds immediately after waking up in the morning before getting out of bed.
function calculateFatBurnZone() {
var age = document.getElementById("userAge").value;
var resting = document.getElementById("restingHR").value;
var resultArea = document.getElementById("hrResultArea");
var maxHRField = document.getElementById("maxHRVal");
var fatBurnField = document.getElementById("fatBurnRange");
var cardioField = document.getElementById("cardioRange");
var adviceField = document.getElementById("zoneAdvice");
if (!age || age 120) {
alert("Please enter a valid age.");
return;
}
var mhr = 220 – age;
var rhr = parseFloat(resting) || 0;
var fatLow, fatHigh, cardioLow, cardioHigh;
if (rhr > 0 && rhr < mhr) {
// Karvonen Formula
var hrr = mhr – rhr;
fatLow = Math.round((hrr * 0.60) + rhr);
fatHigh = Math.round((hrr * 0.70) + rhr);
cardioLow = Math.round((hrr * 0.70) + rhr + 1);
cardioHigh = Math.round((hrr * 0.85) + rhr);
} else {
// Standard Percentage of MHR
fatLow = Math.round(mhr * 0.60);
fatHigh = Math.round(mhr * 0.70);
cardioLow = Math.round(mhr * 0.70) + 1;
cardioHigh = Math.round(mhr * 0.85);
}
maxHRField.innerHTML = mhr;
fatBurnField.innerHTML = fatLow + " – " + fatHigh;
cardioField.innerHTML = cardioLow + " – " + cardioHigh;
adviceField.innerHTML = "To maximize fat loss, aim to keep your heart rate between " + fatLow + " and " + fatHigh + " BPM for at least 30-45 minutes. If your heart rate goes above " + cardioHigh + " BPM, you are entering the anaerobic zone, which improves athletic performance but may be harder to sustain for long weight-loss sessions.";
resultArea.style.display = "block";
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}