Heart Rate Reserve Percentage Calculator

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Heart Rate Reserve (HRR) Calculator

Calculate your Target Heart Rate using the Karvonen Formula.

Moderate: 50-70% | Vigorous: 70-85%

Your Results

Estimated Max HR 0 BPM
Heart Rate Reserve 0 BPM
Target Heart Rate for Specified Intensity 0 BPM

Understanding Heart Rate Reserve (HRR)

Heart Rate Reserve (HRR) is the difference between your measured or predicted maximum heart rate and your resting heart rate. It represents the range of heart beats per minute that are available for exercise.

The Karvonen Formula

The Karvonen method is considered more accurate for determining target heart rate zones than simply calculating a percentage of your maximum heart rate because it accounts for individual fitness levels (via your resting heart rate). The formula is:

Target HR = ((Max HR − Resting HR) × % Intensity) + Resting HR

How to Find Your Inputs

  • Resting Heart Rate: Measure this first thing in the morning before getting out of bed. Count your pulse for 60 seconds.
  • Max Heart Rate: This calculator uses the standard "220 – Age" estimation. For a more precise figure, a clinical stress test is required.
  • Intensity Levels:
    • Moderate intensity: 50% to 70% of HRR
    • Vigorous intensity: 70% to 85% of HRR

Calculation Example

If you are 40 years old with a resting heart rate of 60 BPM and want to train at 70% intensity:

  1. Max HR: 220 – 40 = 180 BPM
  2. Heart Rate Reserve: 180 – 60 = 120 BPM
  3. Target HR: (120 × 0.70) + 60 = 144 BPM
function calculateHRR() { var age = parseFloat(document.getElementById("hrrAge").value); var restingHR = parseFloat(document.getElementById("hrrResting").value); var intensity = parseFloat(document.getElementById("hrrIntensity").value); var resultArea = document.getElementById("hrrResultArea"); if (isNaN(age) || isNaN(restingHR) || isNaN(intensity) || age <= 0 || restingHR <= 0 || intensity <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // 1. Estimate Max HR (Standard Formula: 220 – Age) var maxHR = 220 – age; // 2. Calculate Heart Rate Reserve (HRR) var hrr = maxHR – restingHR; if (hrr <= 0) { alert("Your resting heart rate cannot be higher than your maximum heart rate. Please check your inputs."); return; } // 3. Calculate Target HR using Karvonen Formula // Target HR = ((Max HR − Resting HR) × %Intensity) + Resting HR var targetHR = (hrr * (intensity / 100)) + restingHR; // Display Results document.getElementById("resMaxHR").innerText = Math.round(maxHR); document.getElementById("resHRR").innerText = Math.round(hrr); document.getElementById("resTargetHR").innerText = Math.round(targetHR); resultArea.style.display = "block"; }

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