Zone 2 Calculator Heart Rate

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Zone 2 Heart Rate Calculator (Karvonen Method)

Best measured first thing in the morning before getting out of bed.
function calculateZone2HR() { // Get input values var ageInput = document.getElementById('z2-age').value; var rhrInput = document.getElementById('z2-rhr').value; var resultDiv = document.getElementById('z2-result'); // Parse inputs var age = parseInt(ageInput); var rhr = parseInt(rhrInput); // Validate inputs if (isNaN(age) || age 120) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Please enter a valid age."; return; } if (isNaN(rhr) || rhr 150) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Please enter a realistic resting heart rate (typically between 30 and 150 BPM)."; return; } // Calculate Maximum Heart Rate (MHR) using standard formula var maxHeartRate = 220 – age; // Calculate Heart Rate Reserve (HRR) var heartRateReserve = maxHeartRate – rhr; // Zone 2 is generally defined as 60% to 70% of Heart Rate Reserve // Formula: (HRR * Intensity %) + RHR var lowerBoundRaw = (heartRateReserve * 0.60) + rhr; var upperBoundRaw = (heartRateReserve * 0.70) + rhr; // Round to nearest whole number for BPM var lowerBound = Math.round(lowerBoundRaw); var upperBound = Math.round(upperBoundRaw); // Display results resultDiv.style.display = "block"; resultDiv.innerHTML = "

Your Zone 2 Target Range:

" + "" + lowerBound + " – " + upperBound + " BPM" + "This range is based on the Karvonen formula, using an estimated maximum heart rate of " + maxHeartRate + " BPM."; }

Understanding Zone 2 Training

Zone 2 training is often referred to as the "aerobic base" building zone. Training in this zone is crucial for developing endurance, improving metabolic health, and increasing the body's efficiency at utilizing fat as a primary fuel source.

Unlike high-intensity interval training (HIIT), Zone 2 efforts are sustainable for long periods. A common practical test for Zone 2 is the "talk test": you should be able to maintain a conversation in full sentences without gasping for air while exercising in this zone.

Why Use the Karvonen Method?

While a simple percentage of your estimated Maximum Heart Rate (MHR) (e.g., 220 minus age) gives a rough estimate, it doesn't account for individual fitness levels. The Karvonen Method used in this calculator is more accurate because it incorporates your Resting Heart Rate (RHR).

By using your Heart Rate Reserve (the difference between your maximum and resting heart rates), the training zones are tailored specifically to your current cardiovascular fitness profile.

Example Calculation

Let's look at an example of how the calculator determines the range for a 45-year-old individual with a resting heart rate of 55 BPM.

  1. Estimate Max Heart Rate (MHR): 220 – 45 (Age) = 175 BPM.
  2. Calculate Heart Rate Reserve (HRR): 175 (MHR) – 55 (RHR) = 120 BPM.
  3. Calculate Zone 2 Lower Limit (60%): (120 x 0.60) + 55 = 72 + 55 = 127 BPM.
  4. Calculate Zone 2 Upper Limit (70%): (120 x 0.70) + 55 = 84 + 55 = 139 BPM.

For this individual, their Zone 2 training window is between 127 and 139 BPM.

How to Use This Information

To reap the benefits of Zone 2 training, aim to keep your heart rate within the calculated range during your endurance sessions (running, cycling, rowing, etc.). These sessions typically last anywhere from 45 minutes to several hours, depending on your training goals. Consistency in this zone is key to building a strong aerobic engine.

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