Optional: Leave blank for standard formula, or fill for Karvonen method (more accurate).
Please enter a valid age between 10 and 100.
Estimated Max Heart Rate: 0 BPM
Heart Rate Reserve: 0 BPM
Zone
Intensity
Range (BPM)
function calculateZones() {
// 1. Get Inputs
var ageInput = document.getElementById('hr_age');
var restingInput = document.getElementById('hr_resting');
var errorDiv = document.getElementById('error-message');
var resultsDiv = document.getElementById('results-area');
var age = parseFloat(ageInput.value);
var rhr = parseFloat(restingInput.value);
// 2. Validation
if (isNaN(age) || age 120) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
resultsDiv.style.display = 'block';
// 3. Calculation Logic
// Calculate Max Heart Rate (MHR) = 220 – Age
var maxHR = 220 – age;
document.getElementById('display-mhr').innerHTML = maxHR;
var useKarvonen = !isNaN(rhr) && rhr > 30 && rhr < maxHR;
var hrr = 0;
if (useKarvonen) {
// Heart Rate Reserve (HRR) = Max HR – Resting HR
hrr = maxHR – rhr;
document.getElementById('hrr-display').style.display = 'block';
document.getElementById('display-hrr').innerHTML = hrr;
} else {
document.getElementById('hrr-display').style.display = 'none';
}
// Zone Definitions
// Structure: [Name, Min%, Max%, Description]
var zones = [
{ name: "Zone 1", label: "Very Light", min: 0.50, max: 0.60, desc: "Warm up, recovery, very easy." },
{ name: "Zone 2", label: "Light", min: 0.60, max: 0.70, desc: "Fat burning, endurance base building." },
{ name: "Zone 3", label: "Moderate", min: 0.70, max: 0.80, desc: "Aerobic fitness, improves circulation." },
{ name: "Zone 4", label: "Hard", min: 0.80, max: 0.90, desc: "Anaerobic, increases performance capacity." },
{ name: "Zone 5", label: "Maximum", min: 0.90, max: 1.00, desc: "VO2 Max, peak effort, short intervals." }
];
var tableBody = document.getElementById('zones-body');
tableBody.innerHTML = ''; // Clear previous results
// 4. Loop and Generate Table
for (var i = 0; i < zones.length; i++) {
var z = zones[i];
var minBPM, maxBPM;
if (useKarvonen) {
// Karvonen Formula: Target = (HRR * %) + RHR
minBPM = Math.round((hrr * z.min) + rhr);
maxBPM = Math.round((hrr * z.max) + rhr);
} else {
// Standard Formula: Target = MHR * %
minBPM = Math.round(maxHR * z.min);
maxBPM = Math.round(maxHR * z.max);
}
// Create Table Row
var row = document.createElement('tr');
row.className = 'zone-row';
row.innerHTML = '
' + z.name + '' + z.label + '
' +
'
' + (z.min * 100) + '% – ' + (z.max * 100) + '%
' +
'
' + minBPM + ' – ' + maxBPM + ' bpm
';
tableBody.appendChild(row);
}
}
Everything You Need to Know About Heart Rate Zones
Understanding your heart rate zones is the key to training smarter, not just harder. Whether you are a marathon runner, a cyclist, or someone just starting their fitness journey, using a heart rate zone calculator allows you to target specific physiological adaptations. Instead of guessing your effort level, you can use biological data to ensure you are burning fat, building endurance, or increasing your VO2 max.
Why Use a Heart Rate Zone Calculator?
Your heart rate acts as a tachometer for your body. Just as you wouldn't drive a car in the red line constantly, you shouldn't exercise at maximum effort for every workout. By dividing your heart rate intensities into five distinct zones, you can structure a training plan that balances stress and recovery.
Prevent Overtraining: Spending too much time in high zones (Zone 4 and 5) without recovery can lead to burnout and injury.
Maximize Fat Loss: Zone 2 is often cited as the "fat-burning zone" because the body primarily utilizes fat for fuel at this lower intensity.
Improve Cardiovascular Health: Varied training across zones strengthens the heart muscle and improves blood vessel elasticity.
Understanding the 5 Heart Rate Zones
This calculator breaks down your training intensity into five standard zones based on your Maximum Heart Rate (MHR). Here is what each zone accomplishes:
Zone 1: Very Light (50-60%)
This is your warm-up and cool-down zone. Training here aids in recovery by increasing blood flow to muscles to flush out waste products like lactate without placing significant stress on the body. You should be able to hold a conversation effortlessly.
Zone 2: Light (60-70%)
Ideally, 70-80% of your training should happen here. This is the foundation of endurance. In Zone 2, you build mitochondrial density and teach your body to burn fat efficiently. It feels easy, but sustaining it for a long duration builds a massive "aerobic engine."
Zone 3: Moderate (70-80%)
Often called the "grey zone." It is harder than Zone 2 but not hard enough to trigger the high-performance adaptations of Zone 4. While it improves aerobic fitness, spending too much time here can cause fatigue without the specific benefits of the other zones.
Zone 4: Hard (80-90%)
This is the anaerobic threshold zone. Here, you are training your body to tolerate and clear lactate. Breathing becomes heavy and labored. Training in Zone 4 improves your speed endurance and your ability to sustain high-intensity efforts.
Zone 5: Maximum (90-100%)
This zone is reserved for all-out efforts, typically lasting only a few seconds to a few minutes. It targets your neuromuscular system and VO2 max. This is extremely taxing and should be used sparingly in training.
The Calculation Methods: Standard vs. Karvonen
This tool utilizes two different methods depending on the data you provide:
Standard Method (Age Predicted): This uses the formula 220 – Age to find your Max Heart Rate, then calculates percentages of that number. It is a good baseline if you do not know your resting heart rate.
Karvonen Formula (Heart Rate Reserve): If you enter your Resting Heart Rate (RHR), the calculator switches to this method. It is far more accurate for individuals with higher or lower fitness levels because it takes into account your "Heart Rate Reserve" (the difference between your Max and Resting HR).
To get the most accurate results from this calculator, measure your pulse immediately after waking up in the morning, before you get out of bed or drink coffee. Count the beats for 60 seconds. Do this for 3-4 days and take the average.