.hr-calc-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e1e1e1;
border-radius: 12px;
background-color: #ffffff;
color: #333;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.hr-calc-header {
text-align: center;
margin-bottom: 25px;
}
.hr-calc-header h2 {
color: #d32f2f;
margin-bottom: 10px;
}
.hr-calc-form {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
margin-bottom: 25px;
}
@media (max-width: 600px) {
.hr-calc-form { grid-template-columns: 1fr; }
}
.hr-calc-group {
display: flex;
flex-direction: column;
}
.hr-calc-group label {
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
}
.hr-calc-group input {
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 16px;
}
.hr-calc-btn {
grid-column: 1 / -1;
background-color: #d32f2f;
color: white;
padding: 15px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background 0.3s;
}
.hr-calc-btn:hover {
background-color: #b71c1c;
}
.hr-calc-results {
margin-top: 30px;
padding: 20px;
background-color: #f9f9f9;
border-radius: 8px;
display: none;
}
.hr-calc-results h3 {
margin-top: 0;
color: #333;
border-bottom: 2px solid #d32f2f;
padding-bottom: 10px;
}
.result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.result-row:last-child { border-bottom: none; }
.result-label { font-weight: 600; }
.result-value { color: #d32f2f; font-weight: bold; }
.hr-article {
margin-top: 40px;
line-height: 1.6;
color: #444;
}
.hr-article h3 { color: #333; margin-top: 25px; }
.hr-article table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
.hr-article th, .hr-article td {
text-align: left;
padding: 12px;
border-bottom: 1px solid #ddd;
}
.hr-article th { background-color: #f4f4f4; }
Your Heart Rate Profile
Maximum Heart Rate (MHR):
—
Heart Rate Reserve (HRR):
—
Target Intensity Zones:
Zone 1: Recovery (50-60%)
—
Zone 2: Fat Burn (60-70%)
—
Zone 3: Aerobic (70-80%)
—
Zone 4: Anaerobic (80-90%)
—
Zone 5: Red Line (90-100%)
—
Understanding How Heart Rate is Calculated
Knowing how your heart rate is calculated is fundamental for effective cardiovascular training. Your heart rate, measured in Beats Per Minute (BPM), serves as a direct indicator of how hard your cardiovascular system is working during physical activity.
The Primary Formulas
There are two main methods used to determine your training targets:
- The Fox Formula: This is the simplest method where Maximum Heart Rate = 220 – Age. While widely used, it does not account for individual fitness levels.
- The Karvonen Formula: This is the method used by our calculator above. It is considered more accurate because it incorporates your Resting Heart Rate (RHR) to calculate your Heart Rate Reserve (HRR).
The Math Behind the Karvonen Formula
To find a specific target heart rate zone, the formula is:
Target HR = [(Max HR − Resting HR) × %Intensity] + Resting HR
Example Calculation
Imagine a 40-year-old individual with a resting heart rate of 60 BPM who wants to train at 70% intensity (Aerobic Zone):
- Max HR: 220 – 40 = 180 BPM
- Heart Rate Reserve (HRR): 180 – 60 = 120 BPM
- Target Zone: (120 × 0.70) + 60 = 144 BPM
Training Zones Explained
| Zone |
Intensity |
Benefit |
| Zone 1 |
50-60% |
Warm-up and active recovery. |
| Zone 2 |
60-70% |
Weight control and base endurance. |
| Zone 3 |
70-80% |
Improving cardiovascular fitness. |
| Zone 4 |
80-90% |
Increased speed and anaerobic capacity. |
| Zone 5 |
90-100% |
Maximal effort and sprinting power. |
Why Resting Heart Rate Matters
Your Resting Heart Rate is typically measured first thing in the morning before you get out of bed. A lower resting heart rate usually indicates a more efficient heart and better cardiovascular fitness. By including this in the calculation, the Karvonen formula provides a personalized range that evolves as your fitness improves.
function calculateHeartRate() {
var age = parseFloat(document.getElementById('age').value);
var rhr = parseFloat(document.getElementById('rhr').value);
var resultsDiv = document.getElementById('hr-results');
if (isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
if (isNaN(rhr) || rhr 150) {
alert("Please enter a valid resting heart rate (typical range 30-150).");
return;
}
// Calculations
var mhr = 220 – age;
var hrr = mhr – rhr;
if (hrr <= 0) {
alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs.");
return;
}
// Karvonen Formula: ((MHR – RHR) * %Intensity) + RHR
function getZoneRange(minPct, maxPct, hrReserve, restHR) {
var low = Math.round((hrReserve * minPct) + restHR);
var high = Math.round((hrReserve * maxPct) + restHR);
return low + " – " + high + " BPM";
}
// Update UI
document.getElementById('res-mhr').innerText = mhr + " BPM";
document.getElementById('res-hrr').innerText = hrr + " BPM";
document.getElementById('zone1').innerText = getZoneRange(0.50, 0.60, hrr, rhr);
document.getElementById('zone2').innerText = getZoneRange(0.60, 0.70, hrr, rhr);
document.getElementById('zone3').innerText = getZoneRange(0.70, 0.80, hrr, rhr);
document.getElementById('zone4').innerText = getZoneRange(0.80, 0.90, hrr, rhr);
document.getElementById('zone5').innerText = getZoneRange(0.90, 1.00, hrr, rhr);
resultsDiv.style.display = 'block';
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}