Find your optimal "Fat Burning Zone" based on your age and fitness level.
Weight Loss (60-70%)
Aerobic/Fitness (70-80%)
Performance (80-90%)
Male
Female
Your Target Results:
Your Estimated Maximum Heart Rate: BPM
Your Target Heart Rate Range for Weight Loss:
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Understanding the Fat Burning Zone
To maximize weight loss, you need to exercise at an intensity that encourages your body to use fat as its primary fuel source. This is typically achieved when your heart rate is between 60% and 70% of your maximum heart rate.
The Karvonen Formula
Our calculator uses the Karvonen Formula, which is considered more accurate than simple percentages because it takes your Resting Heart Rate (RHR) into account. The formula is:
For this individual, the ideal weight loss zone is 138 to 151 beats per minute.
Intensity Zones Overview
Zone
% of Max HR
Benefit
Weight Loss
60% – 70%
Develops basic endurance and burns fat.
Aerobic
70% – 80%
Improves cardiovascular fitness and muscle strength.
Anaerobic
80% – 90%
Increases lactic acid tolerance and high-speed endurance.
function calculateTargetHeartRate() {
var age = parseFloat(document.getElementById('hrAge').value);
var restingHR = parseFloat(document.getElementById('hrResting').value);
var intensityType = document.getElementById('hrIntensity').value;
var resultBox = document.getElementById('hrResult');
if (isNaN(age) || age 120) {
alert('Please enter a valid age.');
return;
}
if (isNaN(restingHR) || restingHR 150) {
alert('Please enter a valid resting heart rate (usually 40-100 BPM).');
return;
}
// Step 1: Calculate Max Heart Rate (Gellish Formula: 207 – (0.7 * age) is often more accurate than 220-age)
// Using standard 220-age for broad compatibility but ensuring it's not negative
var maxHR = 220 – age;
// Step 2: Heart Rate Reserve
var hrr = maxHR – restingHR;
if (hrr <= 0) {
alert('Your resting heart rate cannot be higher than your maximum heart rate. Please check your inputs.');
return;
}
var lowPerc, highPerc, advice;
// Set intensity based on selection
if (intensityType === 'weightloss') {
lowPerc = 0.60;
highPerc = 0.70;
advice = "Stay in this range for 30-60 minutes to optimize fat oxidation.";
} else if (intensityType === 'aerobic') {
lowPerc = 0.70;
highPerc = 0.80;
advice = "This zone improves your cardiovascular endurance and lung capacity.";
} else {
lowPerc = 0.80;
highPerc = 0.90;
advice = "This is a high-intensity zone. Use for interval training (HIIT).";
}
// Karvonen Calculation
var targetLow = Math.round((hrr * lowPerc) + restingHR);
var targetHigh = Math.round((hrr * highPerc) + restingHR);
// Display results
document.getElementById('resMaxHR').innerText = maxHR;
document.getElementById('resTargetRange').innerText = targetLow + " – " + targetHigh + " BPM";
document.getElementById('resAdvice').innerText = "Expert Tip: " + advice;
resultBox.style.display = 'block';
resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}