Zone 2 Calculator Resting Heart Rate

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Zone 2 Training Calculator (Karvonen Method)

Your Zone 2 Target Range

function calculateZone2() { var ageInput = document.getElementById("z2_age").value; var rhrInput = document.getElementById("z2_rhr").value; var resultBox = document.getElementById("z2_result_box"); var outputText = document.getElementById("z2_output_text"); var metricsText = document.getElementById("z2_metrics"); if (ageInput === "" || rhrInput === "" || ageInput <= 0 || rhrInput <= 0) { alert("Please enter valid positive numbers for both age and resting heart rate."); return; } var age = parseInt(ageInput); var rhr = parseInt(rhrInput); // Formula: Karvonen Method // Max Heart Rate (MHR) = 220 – Age // Heart Rate Reserve (HRR) = MHR – RHR // Target HR = (HRR * intensity%) + RHR var mhr = 220 – age; var hrr = mhr – rhr; if (hrr <= 0) { alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs."); return; } // Zone 2 is typically 60% to 70% of Heart Rate Reserve var lowBound = Math.round((hrr * 0.60) + rhr); var highBound = Math.round((hrr * 0.70) + rhr); outputText.innerHTML = lowBound + " – " + highBound + " BPM"; metricsText.innerHTML = "Based on an estimated Max HR of " + mhr + " and HR Reserve of " + hrr + ".Intensity: 60% – 70% of Heart Rate Reserve."; resultBox.style.display = "block"; }

What is Zone 2 Heart Rate Training?

Zone 2 training is a specific level of intensity characterized by "steady-state" aerobic exercise. It is often referred to as the "aerobic base" zone. At this intensity, your body primarily uses fat oxidation (burning fat for fuel) and develops mitochondrial density and efficiency.

The Karvonen Formula vs. Simple Percentage

While many simple calculators just take a percentage of your Max Heart Rate (MHR), this calculator uses the Karvonen Formula. This is widely considered more accurate because it accounts for your Resting Heart Rate (RHR).

By incorporating your RHR, the formula calculates your Heart Rate Reserve (HRR)—the actual range of beats your heart has available for exertion. This provides a much more personalized Zone 2 range for athletes of different fitness levels.

How to Measure Your Resting Heart Rate

For the most accurate calculation, measure your resting heart rate in the morning immediately after waking up, before getting out of bed or consuming caffeine. Use a wearable device or manually count your pulse at your wrist (radial) or neck (carotid) for 60 seconds.

Practical Example Calculation

If you are 40 years old with a resting heart rate of 60 BPM:

  • Max HR: 220 – 40 = 180 BPM
  • Heart Rate Reserve: 180 – 60 = 120 BPM
  • Zone 2 Low (60%): (120 * 0.60) + 60 = 132 BPM
  • Zone 2 High (70%): (120 * 0.70) + 60 = 144 BPM
  • Target Zone: 132 to 144 beats per minute.

Signs You Are in Zone 2

Beyond the numbers, you can use the "Talk Test." In Zone 2, you should be able to hold a full conversation without gasping for air, though you should still feel like you are working. If you can only speak in short sentences, you have likely drifted into Zone 3.

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