Very Light (50%) – Recovery
Light (60%) – Fat Burn
Moderate (70%) – Aerobic/Cardio
Hard (80%) – Anaerobic
Maximum (90%) – VO2 Max
Results:
Your Max Heart Rate: BPM
Target Active Heart Rate: BPM
Understanding Your Active Heart Rate
Active heart rate, often referred to as Target Heart Rate (THR), is the pulse rate you should maintain during aerobic exercise to ensure your heart and lungs receive the most benefit from your workout. While a simple "220 minus age" formula gives a rough estimate of your maximum, the Karvonen formula used in this calculator is significantly more accurate because it incorporates your Heart Rate Reserve (HRR).
How to Calculate Using the Karvonen Formula
To calculate your active heart rate manually, follow these steps:
Step 4: Multiply HRR by your desired intensity (e.g., 0.70 for 70%).
Step 5: Add your RHR back to that number to find your Target Heart Rate.
Heart Rate Training Zones
Zone
Intensity
Benefit
Fat Burning
60% – 70%
Weight management and basic endurance.
Aerobic
70% – 80%
Improving cardiovascular fitness and stamina.
Anaerobic
80% – 90%
Increases speed, power, and lactic acid tolerance.
Practical Example
If you are a 40-year-old with a resting heart rate of 70 BPM and you want to exercise at 75% intensity:
Max Heart Rate: 220 – 40 = 180 BPM
Heart Rate Reserve: 180 – 70 = 110 BPM
Intensity Calculation: 110 x 0.75 = 82.5
Target Active Rate: 82.5 + 70 = 152.5 BPM
In this example, maintaining a heart rate of roughly 152 beats per minute would keep the individual perfectly within their aerobic training zone.
function calculateActiveHR() {
var age = document.getElementById('hr_age').value;
var rhr = document.getElementById('hr_resting').value;
var intensityPercent = document.getElementById('hr_intensity').value;
if (age === "" || rhr === "" || age <= 0 || rhr <= 0) {
alert("Please enter valid positive numbers for age and resting heart rate.");
return;
}
var ageNum = parseFloat(age);
var rhrNum = parseFloat(rhr);
var intensityDec = parseFloat(intensityPercent) / 100;
// Simple Max Heart Rate
var mhr = 220 – ageNum;
// Karvonen Formula: THR = ((MHR – RHR) * %Intensity) + RHR
var hrr = mhr – rhrNum;
var thr = (hrr * intensityDec) + rhrNum;
document.getElementById('max_hr_val').innerText = Math.round(mhr);
document.getElementById('target_hr_val').innerText = Math.round(thr);
var desc = "";
if (intensityPercent == "50") desc = "Very light intensity. Ideal for warm-ups or active recovery sessions.";
if (intensityPercent == "60") desc = "Light intensity. This zone helps improve basic endurance and utilizes fat as a primary fuel source.";
if (intensityPercent == "70") desc = "Moderate intensity. The classic 'cardio' zone for heart health and respiratory efficiency.";
if (intensityPercent == "80") desc = "Hard intensity. This improves your anaerobic threshold and high-intensity performance capacity.";
if (intensityPercent == "90") desc = "Maximum intensity. Used for short intervals to improve maximum speed and oxygen uptake.";
document.getElementById('hr_description').innerText = desc;
document.getElementById('hr_result_box').style.display = "block";
}