#hr-zone-calculator-container h2 { color: #2c3e50; text-align: center; margin-bottom: 25px; }
.input-group { margin-bottom: 20px; }
.input-group label { display: block; font-weight: 600; margin-bottom: 8px; color: #444; }
.input-group input { width: 100%; padding: 12px; border: 1px solid #ccc; border-radius: 6px; box-sizing: border-box; font-size: 16px; transition: border-color 0.3s; }
.input-group input:focus { border-color: #3498db; outline: none; }
.calc-button { width: 100%; padding: 15px; background-color: #e74c3c; color: white; border: none; border-radius: 6px; font-size: 18px; font-weight: bold; cursor: pointer; transition: background-color 0.3s; margin-top: 10px; }
.calc-button:hover { background-color: #c0392b; }
#hr-results { margin-top: 30px; display: none; }
.zone-card { padding: 15px; border-radius: 8px; margin-bottom: 10px; display: flex; justify-content: space-between; align-items: center; color: white; }
.zone-1 { background-color: #3498db; }
.zone-2 { background-color: #2ecc71; }
.zone-3 { background-color: #f1c40f; color: #333; }
.zone-4 { background-color: #e67e22; }
.zone-5 { background-color: #c0392b; }
.zone-info { font-weight: bold; font-size: 1.1em; }
.hr-range { font-size: 1.2em; font-weight: 800; }
.mhr-summary { text-align: center; background: #f8f9fa; padding: 15px; border-radius: 8px; margin-bottom: 20px; border-left: 5px solid #e74c3c; }
.error-msg { color: #e74c3c; font-size: 14px; margin-top: 5px; display: none; }
.article-section { margin-top: 40px; border-top: 1px solid #eee; padding-top: 30px; }
.article-section h3 { color: #2c3e50; margin-top: 25px; }
.article-section p { margin-bottom: 15px; }
.formula-box { background: #f4f4f4; padding: 15px; border-radius: 5px; font-family: monospace; overflow-x: auto; margin: 15px 0; }
Please enter valid values for age and resting heart rate.
How the Heart Rate Zone Calculation Formula Works
Calculating your target heart rate zones is essential for optimizing your cardiovascular training. While many simple calculators use the basic 220 – Age formula, this tool utilizes the Karvonen Formula, which is widely considered more accurate because it accounts for your Resting Heart Rate (RHR).
Target HR = ((Max HR − Resting HR) × %Intensity) + Resting HR
The 5 Training Zones Explained
Zone 1 (50-60% HRR): This is the recovery zone. It feels very easy and is used for warming up, cooling down, or active recovery days. It improves overall health and helps recovery after harder sessions.
Zone 2 (60-70% HRR): Known as the "Fat Burning" or "Base" zone. This intensity can be maintained for long periods. It builds aerobic endurance and trains your body to utilize fat more efficiently as a fuel source.
Zone 3 (70-80% HRR): The aerobic zone. This is where you improve cardiovascular strength and lung capacity. Breathing becomes deeper and conversation becomes harder.
Zone 4 (80-90% HRR): The anaerobic zone. You are working hard, and your body begins to produce lactic acid faster than it can be removed. This improves speed, power, and lactate threshold.
Zone 5 (90-100% HRR): Maximum effort. This zone is typically used for short intervals (HIIT). It develops peak power and speed but cannot be sustained for more than a few minutes.
Calculation Example
Consider a 30-year-old individual with a resting heart rate of 60 BPM:
- Max HR: 220 – 30 = 190 BPM
- Heart Rate Reserve (HRR): 190 – 60 = 130 BPM
- Zone 2 Lower Limit (60%): (130 * 0.60) + 60 = 138 BPM
- Zone 2 Upper Limit (70%): (130 * 0.70) + 60 = 151 BPM
This individual's ideal Zone 2 training range would be between 138 and 151 Beats Per Minute.
function calculateHRZones() {
var age = parseFloat(document.getElementById('hr_age').value);
var rhr = parseFloat(document.getElementById('hr_resting').value);
var error = document.getElementById('error_msg');
var resultsDiv = document.getElementById('hr-results');
if (isNaN(age) || isNaN(rhr) || age 120 || rhr 200) {
error.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
error.style.display = 'none';
// Basic Max HR formula: 220 – Age
var mhr = 220 – age;
// Heart Rate Reserve (HRR)
var hrr = mhr – rhr;
if (hrr <= 0) {
alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs.");
return;
}
// Calculations based on Karvonen Formula
// Zone 1: 50-60%
var z1_low = Math.round((hrr * 0.50) + rhr);
var z1_high = Math.round((hrr * 0.60) + rhr);
// Zone 2: 60-70%
var z2_low = Math.round((hrr * 0.60) + rhr);
var z2_high = Math.round((hrr * 0.70) + rhr);
// Zone 3: 70-80%
var z3_low = Math.round((hrr * 0.70) + rhr);
var z3_high = Math.round((hrr * 0.80) + rhr);
// Zone 4: 80-90%
var z4_low = Math.round((hrr * 0.80) + rhr);
var z4_high = Math.round((hrr * 0.90) + rhr);
// Zone 5: 90-100%
var z5_low = Math.round((hrr * 0.90) + rhr);
var z5_high = mhr;
// Display Values
document.getElementById('summary-mhr').getElementsByTagName('span')[0].innerText = mhr;
document.getElementById('summary-hrr').getElementsByTagName('span')[0].innerText = hrr;
document.getElementById('z1_range').innerText = z1_low + " – " + z1_high + " BPM";
document.getElementById('z2_range').innerText = z2_low + " – " + z2_high + " BPM";
document.getElementById('z3_range').innerText = z3_low + " – " + z3_high + " BPM";
document.getElementById('z4_range').innerText = z4_low + " – " + z4_high + " BPM";
document.getElementById('z5_range').innerText = z5_low + " – " + z5_high + " BPM";
resultsDiv.style.display = 'block';
}