Understanding your heart rate zones is the most effective way to optimize your cardiovascular training. By calculating these zones, you can ensure you are training at the right intensity to meet your specific goals, whether it is endurance building, fat loss, or performance improvement.
The Karvonen Formula
This calculator utilizes the Karvonen Formula, which is widely considered more accurate than simple age-based formulas because it incorporates your Heart Rate Reserve (HRR). HRR is the difference between your maximum heart rate and your resting heart rate. By including your resting pulse, the calculation adapts to your current level of fitness.
Zone 1 (50-60%): Very Light. Best for recovery and initial warm-ups. Improves overall health but not necessarily performance.
Zone 2 (60-70%): Light (The Fat Burn Zone). Ideal for basic endurance training. Your body primarily uses fat for fuel in this zone.
Zone 3 (70-80%): Moderate (Aerobic). Improves blood circulation and strengthens the heart. This is the "sweet spot" for improving cardiovascular capacity.
Zone 4 (80-90%): Hard (Anaerobic). This is where you develop speed and high-intensity endurance. You will feel breathless and your muscles will feel fatigued.
Zone 5 (90-100%): Maximum. Only for short intervals. This improves peak performance and sprinting power.
Example Calculation
If you are 40 years old with a resting heart rate of 60 BPM:
Max Heart Rate (MHR): 220 – 40 = 180 BPM.
Heart Rate Reserve (HRR): 180 – 60 = 120 BPM.
Zone 2 Lower Limit (60%): (120 x 0.60) + 60 = 132 BPM.
Zone 2 Upper Limit (70%): (120 x 0.70) + 60 = 144 BPM.
In this example, to stay in the "Fat Burn" zone, the individual should maintain a pulse between 132 and 144 beats per minute.
function calculateHRZones() {
var age = parseFloat(document.getElementById('userAge').value);
var rhr = parseFloat(document.getElementById('restingHR').value);
var resultsDiv = document.getElementById('hrResults');
var tableBody = document.getElementById('zoneTableBody');
var maxHRDisplay = document.getElementById('maxHRVal');
if (isNaN(age) || age 110) {
alert("Please enter a valid age.");
return;
}
if (isNaN(rhr) || rhr 150) {
alert("Please enter a valid resting heart rate (typically 40-100 BPM).");
return;
}
var mhr = 220 – age;
var hrr = mhr – rhr;
maxHRDisplay.innerHTML = mhr;
tableBody.innerHTML = "";
var zones = [
{ name: "Zone 1", label: "Recovery / Warm up", low: 0.50, high: 0.60, color: "#e3f2fd" },
{ name: "Zone 2", label: "Fat Burn / Endurance", low: 0.60, high: 0.70, color: "#e8f5e9" },
{ name: "Zone 3", label: "Aerobic / Fitness", low: 0.70, high: 0.80, color: "#fffde7" },
{ name: "Zone 4", label: "Anaerobic / Speed", low: 0.80, high: 0.90, color: "#fff3e0" },
{ name: "Zone 5", label: "Red Line / Max", low: 0.90, high: 1.00, color: "#ffebee" }
];
for (var i = 0; i < zones.length; i++) {
var lowBPM = Math.round((hrr * zones[i].low) + rhr);
var highBPM = Math.round((hrr * zones[i].high) + rhr);
var row = document.createElement("tr");
row.style.backgroundColor = zones[i].color;
var cell1 = document.createElement("td");
cell1.style.padding = "12px";
cell1.style.borderBottom = "1px solid #ddd";
cell1.style.fontWeight = "bold";
cell1.innerHTML = zones[i].name;
var cell2 = document.createElement("td");
cell2.style.padding = "12px";
cell2.style.borderBottom = "1px solid #ddd";
cell2.innerHTML = zones[i].label;
var cell3 = document.createElement("td");
cell3.style.padding = "12px";
cell3.style.borderBottom = "1px solid #ddd";
cell3.style.fontWeight = "bold";
cell3.innerHTML = lowBPM + " – " + highBPM + " BPM";
row.appendChild(cell1);
row.appendChild(cell2);
row.appendChild(cell3);
tableBody.appendChild(row);
}
resultsDiv.style.display = "block";
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}