Calculate your target heart rate zones based on the Fox Formula
Zone
Intensity
BPM Range
How to Use the Heart Rate Zones Age Calculator
Understanding your heart rate zones is critical for optimizing your cardiovascular fitness and ensuring your workouts match your goals. This calculator uses the standard Fox Formula (220 – Age) to estimate your Maximum Heart Rate (MHR) and then breaks down the five physiological intensity zones used by athletes and clinicians worldwide.
The Five Heart Rate Training Zones
Training at different intensities triggers different physiological adaptations. Here is a breakdown of what happens in each zone:
Zone 1 (50–60%): Very Light. Best for active recovery and warm-ups. It improves overall health but doesn't significantly build endurance.
Zone 2 (60–70%): Light. The "Fat Burning Zone." This intensity builds basic endurance and helps the body become more efficient at utilizing fat for energy.
Zone 3 (70–80%): Moderate. The Aerobic Zone. This improves blood circulation and strengthens the heart and skeletal muscles. Ideal for building stamina.
Zone 4 (80–90%): Hard. The Anaerobic Zone. Training here increases your lactate threshold and improves high-speed endurance. You will breathe heavily.
Zone 5 (90–100%): Maximum. Reserved for interval training and elite performance. It improves maximum performance and sprinting speed.
Calculated Example for a 40-Year-Old
If you are 40 years old, your estimated Maximum Heart Rate is 180 beats per minute (BPM). Based on this:
Zone 2 (Fat Burn): 108 – 126 BPM
Zone 3 (Aerobic): 126 – 144 BPM
Zone 4 (Anaerobic): 144 – 162 BPM
Why Age-Based Calculations Matter
As we age, our heart's maximum capacity naturally declines. Using a generic target (like "always aim for 150 BPM") can be dangerous for older individuals or ineffective for younger athletes. By using an age-specific calculator, you ensure that your "Moderate" effort is actually moderate for your biological profile. For the most accurate results, athletes often use the Karvonen formula which includes resting heart rate, but the Fox formula remains the gold standard for general fitness populations.
function calculateHRZones() {
var ageInput = document.getElementById('hrAge');
var age = parseFloat(ageInput.value);
var resultsDiv = document.getElementById('hrResults');
var mhrOutput = document.getElementById('mhrOutput');
var zoneBody = document.getElementById('zoneBody');
if (isNaN(age) || age 120) {
alert("Please enter a valid age between 1 and 120.");
return;
}
// Fox Formula
var mhr = 220 – age;
// Calculate Zones
var zones = [
{ name: "Zone 1 (Recovery)", range: "50-60%", min: 0.50, max: 0.60, class: "zone-1", desc: "Very Light" },
{ name: "Zone 2 (Fat Burn)", range: "60-70%", min: 0.60, max: 0.70, class: "zone-2", desc: "Light" },
{ name: "Zone 3 (Aerobic)", range: "70-80%", min: 0.70, max: 0.80, class: "zone-3", desc: "Moderate" },
{ name: "Zone 4 (Anaerobic)", range: "80-90%", min: 0.80, max: 0.90, class: "zone-4", desc: "Hard" },
{ name: "Zone 5 (VO2 Max)", range: "90-100%", min: 0.90, max: 1.00, class: "zone-5", desc: "Maximum" }
];
mhrOutput.innerHTML = "Your Estimated Max Heart Rate: " + mhr + " BPM";
var html = "";
for (var i = 0; i < zones.length; i++) {
var low = Math.round(mhr * zones[i].min);
var high = Math.round(mhr * zones[i].max);
html += "