function calculateHeartRate() {
var ageInput = document.getElementById('ageInput');
var age = parseFloat(ageInput.value);
var gender = document.getElementById('genderSelect').value;
var resultContainer = document.getElementById('result-container');
var mhrDisplay = document.getElementById('mhrDisplay');
var formulaName = document.getElementById('formulaName');
var zonesBody = document.getElementById('zonesBody');
// Validation
if (isNaN(age) || age 120) {
alert("Please enter a valid age between 5 and 120.");
return;
}
// Calculation Logic
// We will calculate a primary MHR to base zones on.
// Standard Fox Formula: 220 – Age
// Gulati Formula (Women): 206 – (0.88 * Age)
// Tanaka Formula: 208 – (0.7 * Age) -> Often considered more accurate for adults over 40.
var mhr = 0;
var formulaUsed = "";
if (gender === 'female') {
// Using Gulati formula for women as it is often cited as more accurate for females
mhr = 206 – (0.88 * age);
formulaUsed = "Gulati (206 – 0.88 × Age)";
} else {
// Using Tanaka formula generally, or Fox. Let's use the Fox formula as the standard baseline
// but for a better calculator, Tanaka is often preferred in modern sports science.
// However, 220-age is the most expected "standard". Let's stick to 220-age for Male/General to match common expectations,
// or switch to Tanaka if we want "Expert" results.
// Let's use the classic Fox formula for general/male to ensure user expectations are met for a standard calculator.
mhr = 220 – age;
formulaUsed = "Fox (220 – Age)";
}
mhr = Math.round(mhr);
// Calculate Zones
// Zone 1: 50-60%
// Zone 2: 60-70%
// Zone 3: 70-80%
// Zone 4: 80-90%
// Zone 5: 90-100%
var z1_min = Math.round(mhr * 0.50);
var z1_max = Math.round(mhr * 0.60);
var z2_min = Math.round(mhr * 0.60);
var z2_max = Math.round(mhr * 0.70);
var z3_min = Math.round(mhr * 0.70);
var z3_max = Math.round(mhr * 0.80);
var z4_min = Math.round(mhr * 0.80);
var z4_max = Math.round(mhr * 0.90);
var z5_min = Math.round(mhr * 0.90);
var z5_max = mhr;
// Display Results
mhrDisplay.innerHTML = mhr + " Beats Per Minute";
formulaName.innerText = formulaUsed;
// Generate Table HTML
var html = ";
html += '
Calculating your Maximum Heart Rate (MHR) is the foundational step in designing an effective and safe cardiovascular training program. Your MHR represents the highest number of beats per minute (BPM) your heart can achieve during maximum physical exertion. While a clinical stress test is the most accurate method to determine this figure, mathematical formulas provide a reliable baseline for most fitness enthusiasts.
Why Heart Rate Zones Matter
Training isn't just about going as fast as you can. Different heart rate intensities trigger different physiological adaptations in the body. By training in specific "zones"—percentages of your MHR—you can target specific fitness goals:
Fat Burning (Zone 2): Lower intensity exercise where the body relies primarily on fat stores for fuel. Ideal for long-duration endurance.
Aerobic Capacity (Zone 3): Improves blood circulation and the heart's efficiency. This is the "sweet spot" for cardiovascular health.
Performance (Zone 4 & 5): High-intensity intervals that improve speed, power, and lactic acid tolerance.
The Formulas Used
This calculator utilizes different formulas depending on the input to provide a relevant estimation:
The Fox Formula (220 – Age): The most widely recognized formula used for decades. It provides a good general estimate for the average population.
The Gulati Formula (206 – 0.88 × Age): Research suggests that the traditional Fox formula often overestimates MHR for women. The Gulati formula is specifically derived for women to provide a more accurate training ceiling.
Safety Considerations
Please remember that these calculations are estimates. Genetics, medications (such as beta-blockers), and overall fitness levels can cause your actual maximum heart rate to deviate from the predicted number. If you are new to exercise or have existing heart conditions, consult a physician before attempting to reach high-intensity heart rate zones.
How to Use This Data
Once you have your zones calculated above, use a heart rate monitor (chest strap or smartwatch) during your workouts. Aim to stay within the BPM range that corresponds to your goal for that session. For example, a recovery run should strictly stay in Zone 1 or 2, while a HIIT session should spike into Zone 4 or 5.