1 Heart Rate Reserve is Used to Calculate

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Heart Rate Reserve (HRR) & Target Heart Rate Calculator

70%

Results

Estimated Max Heart Rate: —
Heart Rate Reserve (HRR): —
Target Heart Rate (THR): —

*Target Heart Rate calculated using the Karvonen Formula.

function calculateHRR() { var age = parseFloat(document.getElementById('userAge').value); var rhr = parseFloat(document.getElementById('restingHR').value); var intensity = parseFloat(document.getElementById('exerciseIntensity').value) / 100; if (isNaN(age) || isNaN(rhr) || age <= 0 || rhr <= 0) { alert("Please enter valid positive numbers for Age and Resting Heart Rate."); return; } // MHR = 220 – Age (Standard Fox Formula) var mhr = 220 – age; // HRR = Max HR – Resting HR var hrr = mhr – rhr; // Karvonen Formula: THR = (HRR * Intensity) + Resting HR var thr = (hrr * intensity) + rhr; document.getElementById('maxHRResult').innerText = Math.round(mhr) + " BPM"; document.getElementById('hrrResult').innerText = Math.round(hrr) + " BPM"; document.getElementById('targetHRResult').innerText = Math.round(thr) + " BPM"; document.getElementById('hrr-results').style.display = 'block'; }

What is 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 actual range of heart beats available for use during physical activity. Unlike simply calculating a percentage of your maximum heart rate, HRR provides a more personalized metric because it accounts for your cardiovascular fitness level through your resting heart rate.

The Karvonen Formula: How It Is Used

In exercise physiology, 1 heart rate reserve is used to calculate the Target Heart Rate (THR) for specific training intensities. The Karvonen Formula is widely considered more accurate than the standard "percentage of maximum heart rate" method because it scales the intensity based on your individual physiological baseline.

The Formula:
Target Heart Rate = [(Max HR − Resting HR) × %Intensity] + Resting HR

Why Calculating HRR Matters

Athletes and fitness enthusiasts use HRR to ensure they are training within specific "zones" to achieve different physiological outcomes:

  • Fat Burning Zone (50% – 60% HRR): Ideal for beginners or long-duration endurance recovery.
  • Aerobic/Cardio Zone (70% – 80% HRR): Improves cardiovascular health and respiratory capacity.
  • Anaerobic Zone (80% – 90% HRR): Increases lactic acid tolerance and speed.

Example Calculation

Imagine a 40-year-old individual with a resting heart rate of 60 BPM who wants to exercise at 70% intensity:

  1. Estimated Max HR: 220 – 40 = 180 BPM
  2. Heart Rate Reserve: 180 – 60 = 120 BPM
  3. Target Heart Rate: (120 × 0.70) + 60 = 144 BPM

In this case, 144 BPM is the specific target this individual should aim for during their workout to maintain a 70% effort level relative to their fitness capacity.

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