Calculate your maximum heart rate and identify the optimal fat-burning zones based on your age and weight.
Male
Female
Leave blank for standard formula
0Estimated Maximum Heart Rate (BPM)
Target Heart Rate Zones & Calorie Burn
Estimated calories burned per hour based on your weight input.
Zone Name
Intensity
Heart Rate (BPM)
Est. Calories/Hr
Understanding Max Heart Rate and Weight Management
When determining the efficacy of a workout, particularly for weight loss, understanding your Maximum Heart Rate (MHR) is the foundational step. While your body weight does not directly dictate your maximum heart rate (which is primarily determined by age and genetics), it plays a crucial role in how much energy (calories) you expend while training in specific heart rate zones.
The Relationship Between Heart Rate and Weight
Many individuals confuse the mechanics of MHR with weight. Here is the distinction:
Heart Rate: Generally calculated as 220 - Age. It decreases as you get older regardless of your size.
Weight's Role: Heavier individuals burn more calories at the same heart rate compared to lighter individuals. This is because moving a larger mass requires more kinetic energy.
The "Fat Burning" Zone Explained
You will often hear about the "Fat Burning Zone," which is typically Zone 2 (60-70% of your MHR). In this zone, the body relies primarily on fat oxidation for fuel rather than glycogen (carbs).
However, for total weight loss, total calorie burn matters most. While Zone 2 burns a higher percentage of fat, Zone 3 or 4 (Cardio/Aerobic) burns more total calories per minute. This calculator estimates your calorie burn based on your specific weight input to help you balance intensity with duration.
Formulas Used
This calculator utilizes two primary methods depending on your inputs:
Fox Formula: The standard 220 - Age for MHR estimation.
Karvonen Method: If you input your Resting Heart Rate (RHR), we use the Heart Rate Reserve (HRR) method. This is more accurate as it accounts for your fitness level.
Keytel Formula: Used to estimate caloric expenditure based on age, gender, weight, and heart rate intensity.
Safety Considerations
Before starting any vigorous exercise program based on these zones, consult a physician, especially if you have a history of heart conditions or are significantly overweight. These numbers are estimates and individual physiology can vary.
function calculateHeartMetrics() {
// 1. Get Inputs
var ageInput = document.getElementById('inputAge');
var weightInput = document.getElementById('inputWeight');
var genderInput = document.getElementById('inputGender');
var rhrInput = document.getElementById('inputRHR');
var age = parseFloat(ageInput.value);
var weightLbs = parseFloat(weightInput.value);
var gender = genderInput.value;
var rhr = parseFloat(rhrInput.value);
// 2. Validation
if (isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
if (isNaN(weightLbs) || weightLbs 0 && rhr < mhr;
var hrr = 0; // Heart Rate Reserve
if (useKarvonen) {
hrr = mhr – rhr;
}
// 5. Define Zones
// Zones: 1: 50-60%, 2: 60-70%, 3: 70-80%, 4: 80-90%, 5: 90-100%
var zones = [
{ name: "Warm Up / Recovery", minPct: 0.50, maxPct: 0.60, class: "tag-warmup", desc: "Very Light" },
{ name: "Fat Burn / Weight Loss", minPct: 0.60, maxPct: 0.70, class: "tag-fatburn", desc: "Light", isTarget: true },
{ name: "Aerobic / Cardio", minPct: 0.70, maxPct: 0.80, class: "tag-cardio", desc: "Moderate" },
{ name: "Anaerobic", minPct: 0.80, maxPct: 0.90, class: "tag-hard", desc: "Hard" },
{ name: "VO2 Max", minPct: 0.90, maxPct: 1.00, class: "tag-max", desc: "Maximum" }
];
// 6. Generate Table HTML
var tableHtml = "";
// Convert weight to KG for calorie formula
var weightKg = weightLbs * 0.453592;
for (var i = 0; i < zones.length; i++) {
var z = zones[i];
// Calculate BPM Range
var minBpm, maxBpm;
if (useKarvonen) {
// Target Heart Rate = ((max HR − resting HR) × %Intensity) + resting HR
minBpm = Math.round((hrr * z.minPct) + rhr);
maxBpm = Math.round((hrr * z.maxPct) + rhr);
} else {
// Standard % of MHR
minBpm = Math.round(mhr * z.minPct);
maxBpm = Math.round(mhr * z.maxPct);
}
// Calculate Average BPM for this zone for calorie math
var avgZoneBpm = (minBpm + maxBpm) / 2;
// Calculate Calories Burned per Hour (Keytel Formula Estimate)
// Male: ((-55.0969 + (0.6309 x HR) + (0.1988 x W) + (0.2017 x A))/4.184) x 60
// Female: ((-20.4022 + (0.4472 x HR) – (0.1263 x W) + (0.074 x A))/4.184) x 60
var calsPerMin = 0;
if (gender === "male") {
calsPerMin = ((-55.0969 + (0.6309 * avgZoneBpm) + (0.1988 * weightKg) + (0.2017 * age)) / 4.184);
} else {
calsPerMin = ((-20.4022 + (0.4472 * avgZoneBpm) – (0.1263 * weightKg) + (0.074 * age)) / 4.184);
}
// Safety check for negative calories (if formula bounds are exceeded weirdly)
if (calsPerMin < 0) calsPerMin = 0;
var calsPerHour = Math.round(calsPerMin * 60);
// Row Styling
var rowClass = z.isTarget ? "zone-highlight" : "";
tableHtml += "