Calculate your optimal heart rate zones using the Karvonen Formula.
Measure your pulse for 60 seconds while completely relaxed, preferably in the morning.
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Max Heart Rate (BPM)
0
Heart Rate Reserve
Your Training Zones
Zone
Intensity
Target Range (BPM)
Benefit
How to Calculate Heart Rate for Cardio Exercise
Effective cardio training relies on intensity. If your heart rate is too low, you may not achieve your fitness goals efficiently. If it is too high, you risk injury or burnout. This calculator uses the Karvonen Formula, widely considered the gold standard for determining personal exercise intensity zones because it accounts for your resting heart rate, not just your age.
Understanding the Variables
Maximum Heart Rate (MHR): Estimated as 220 minus your age. This is the theoretical limit of your heart beats per minute.
Resting Heart Rate (RHR): Your heart rate when you are completely at rest. A lower RHR generally indicates better cardiovascular fitness.
Heart Rate Reserve (HRR): The difference between your MHR and RHR. This represents the full range of your heart's functional capacity.
The 5 Heart Rate Zones
Training in specific zones yields different metabolic benefits:
Zone 1 (50-60%): Very light intensity. Used for warm-ups and active recovery. Helps improve overall health and aids recovery.
Zone 2 (60-70%): Light intensity. Often called the "Fat Burning Zone." It builds basic endurance and burns a higher percentage of calories from fat.
Zone 3 (70-80%): Moderate intensity. Improves aerobic fitness and blood circulation. This is the sweet spot for general cardio training.
Zone 4 (80-90%): Hard intensity. Increases anaerobic capacity and tolerance to lactic acid. Used for short bursts of speed or power.
Zone 5 (90-100%): Maximum intensity. Only sustainable for very short periods. Used primarily by elite athletes for interval training.
How to Use These Numbers
To use these results, wear a heart rate monitor or smartwatch during your exercise. For a steady-state cardio workout (like jogging or cycling), aim to keep your heart rate within Zone 2 or Zone 3. For High-Intensity Interval Training (HIIT), you will fluctuate between Zone 4 (during work intervals) and Zone 1 or 2 (during rest intervals).
function calculateZones() {
// Get Inputs
var ageInput = document.getElementById("inputAge");
var rhrInput = document.getElementById("inputRHR");
var resultContainer = document.getElementById("hr-result-container");
var mhrDisplay = document.getElementById("res-mhr");
var hrrDisplay = document.getElementById("res-hrr");
var tableBody = document.getElementById("res-table-body");
var age = parseFloat(ageInput.value);
var rhr = parseFloat(rhrInput.value);
// Validation
if (isNaN(age) || age 120) {
alert("Please enter a valid age between 1 and 120.");
return;
}
if (isNaN(rhr) || rhr 200) {
alert("Please enter a valid resting heart rate (usually between 30 and 150 bpm).");
return;
}
// Logic: Karvonen Formula
// 1. Calculate Max Heart Rate (MHR)
var mhr = 220 – age;
// 2. Calculate Heart Rate Reserve (HRR)
var hrr = mhr – rhr;
// 3. Define Zones (Intensity ranges)
var zones = [
{ id: 1, minPct: 0.50, maxPct: 0.60, name: "Zone 1", desc: "Warm Up / Recovery", color: "#9e9e9e" },
{ id: 2, minPct: 0.60, maxPct: 0.70, name: "Zone 2", desc: "Fat Burn / Endurance", color: "#4caf50" },
{ id: 3, minPct: 0.70, maxPct: 0.80, name: "Zone 3", desc: "Aerobic / Cardio", color: "#ff9800" },
{ id: 4, minPct: 0.80, maxPct: 0.90, name: "Zone 4", desc: "Anaerobic / Hard", color: "#ff5722" },
{ id: 5, minPct: 0.90, maxPct: 1.00, name: "Zone 5", desc: "VO2 Max / Peak", color: "#d32f2f" }
];
// Clear previous results
tableBody.innerHTML = "";
// Loop through zones and calculate specific BPM targets
// Formula: Target HR = (HRR * intensity) + RHR
for (var i = 0; i < zones.length; i++) {
var zone = zones[i];
var minBpm = Math.round((hrr * zone.minPct) + rhr);
var maxBpm = Math.round((hrr * zone.maxPct) + rhr);
var row = document.createElement("tr");
row.className = "hr-zone-row";
row.innerHTML =
'