function calculateHeartRate() {
// 1. Get Inputs
var age = parseInt(document.getElementById('hrAge').value);
var gender = document.getElementById('hrGender').value;
var restingHr = parseInt(document.getElementById('restHr').value);
var method = document.getElementById('calcMethod').value;
var resultDiv = document.getElementById('hrResult');
// 2. Validation
if (!age || isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
// 3. Calculate MHR (Max Heart Rate) based on formula
var mhr = 0;
var formulaText = "";
// Auto-switch to Gulati if user selects Gulati but is Male (warn/correct) or general logic
if (method === 'gulati' && gender === 'male') {
// If male selects Gulati, default back to Tanaka or Standard as Gulati is specifically derived for women
method = 'tanaka';
}
if (method === 'standard') {
// Fox Formula
mhr = 220 – age;
formulaText = "Based on Standard Formula (220 – Age)";
} else if (method === 'tanaka') {
// Tanaka Formula
mhr = 208 – (0.7 * age);
formulaText = "Based on Tanaka Formula (208 – 0.7 × Age)";
} else if (method === 'gulati') {
// Gulati Formula (Best for women)
mhr = 206 – (0.88 * age);
formulaText = "Based on Gulati Formula (206 – 0.88 × Age)";
}
mhr = Math.round(mhr);
// 4. Calculate Zones
// Determine if we use Karvonen (HR Reserve) or straight Percentage
var useKarvonen = !isNaN(restingHr) && restingHr > 0;
var zoneHtml = "";
var explanation = useKarvonen
? "Calculated using the Karvonen Method (Heart Rate Reserve) for higher accuracy tailored to your fitness level."
: "Calculated using standard percentage of Max Heart Rate.";
// Define Zone Percentages [min, max, Label, Class, Benefit]
var zones = [
[0.50, 0.60, "Zone 1", "zone-1", "Warm up / Recovery"],
[0.60, 0.70, "Zone 2", "zone-2", "Fat Burning / Endurance"],
[0.70, 0.80, "Zone 3", "zone-3", "Aerobic Fitness"],
[0.80, 0.90, "Zone 4", "zone-4", "Anaerobic / Performance"],
[0.90, 1.00, "Zone 5", "zone-5", "Maximum Effort"]
];
for (var i = 0; i < zones.length; i++) {
var minPct = zones[i][0];
var maxPct = zones[i][1];
var zLabel = zones[i][2];
var zClass = zones[i][3];
var zBenefit = zones[i][4];
var minBpm, maxBpm;
if (useKarvonen) {
// Target Heart Rate = ((MHR − Resting HR) × %Intensity) + Resting HR
var hrr = mhr – restingHr;
minBpm = Math.round((hrr * minPct) + restingHr);
maxBpm = Math.round((hrr * maxPct) + restingHr);
} else {
// Straight % of MHR
minBpm = Math.round(mhr * minPct);
maxBpm = Math.round(mhr * maxPct);
}
zoneHtml += `
How Do You Calculate Your Maximum Heart Rate for Exercise?
Understanding your Maximum Heart Rate (MHR) is the cornerstone of safe and effective cardiovascular training. Whether you are training for a marathon, trying to burn fat, or simply maintaining heart health, knowing your heart rate zones ensures you aren't under-training or over-exerting yourself.
Why it matters: Training at specific percentages of your MHR triggers different metabolic adaptations. Low intensity burns fat, while high intensity improves VO2 max and speed.
Common Methods to Calculate Max Heart Rate
While a clinical stress test is the most accurate way to determine MHR, several mathematical formulas provide reliable estimates for the general population.
1. The Fox Formula (The Standard)
This is the most widely used formula found on gym machines and basic fitness trackers. It is simple but can have a margin of error of +/- 10-12 beats per minute (BPM).
MHR = 220 – Age
2. The Tanaka Formula
Developed to be more accurate for healthy adults across a wider age range. It tends to calculate a slightly higher max heart rate for older adults compared to the Fox formula.
MHR = 208 – (0.7 × Age)
3. The Gulati Formula (For Women)
Research has shown that the standard formulas often overestimate MHR in women. Martha Gulati et al. derived a formula specifically for women to provide a safer target zone.
MHR = 206 – (0.88 × Age)
Understanding the Karvonen Method
Standard calculations look at a percentage of your absolute max. However, the Karvonen Method incorporates your Resting Heart Rate (RHR) to calculate your "Heart Rate Reserve" (HRR).
This method is considered more accurate for individuals with varying fitness levels. For example, a fit athlete has a lower resting heart rate and a larger heart rate reserve than a sedentary person of the same age.
Once you have your MHR, you can target specific zones:
Zone 1 (50-60%): Very light activity, warm-up, recovery. Helps with blood flow and muscle recovery.
Zone 2 (60-70%): Light aerobic activity. The "fat burning" zone where the body learns to use fat as fuel efficiently.
Zone 3 (70-80%): Moderate aerobic activity. Improves blood circulation and skeletal muscle efficiency.
Zone 4 (80-90%): Hard anaerobic activity. Increases speed endurance and tolerance to lactic acid.
Zone 5 (90-100%): Maximum effort. Short bursts used for interval training to increase power.
Safety Note: Always consult with a healthcare professional before starting a new exercise regimen, especially if you have a history of heart conditions or high blood pressure.