Heart Rate Reserve Calculation Formula

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Heart Rate Reserve (HRR) Calculator

Your Results:

Estimated Max HR: BPM

Heart Rate Reserve (HRR): BPM

Target Heart Rate (at %): BPM

function calculateHRR() { var age = parseFloat(document.getElementById('age').value); var restingHR = parseFloat(document.getElementById('restingHR').value); var intensity = parseFloat(document.getElementById('intensity').value); var resultsDiv = document.getElementById('hrr-results'); if (isNaN(age) || isNaN(restingHR) || isNaN(intensity) || age <= 0 || restingHR <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Max Heart Rate Formula (Fox Formula: 220 – Age) var maxHR = 220 – age; // Heart Rate Reserve Formula (HRR = Max HR – Resting HR) var hrr = maxHR – restingHR; if (hrr <= 0) { alert("Resting heart rate cannot be higher than maximum heart rate. Please check your inputs."); return; } // Karvonen Formula for Target Heart Rate // THR = (HRR * Intensity%) + Resting HR var targetHR = (hrr * (intensity / 100)) + restingHR; document.getElementById('maxHRVal').innerText = Math.round(maxHR); document.getElementById('hrrVal').innerText = Math.round(hrr); document.getElementById('intensityVal').innerText = intensity; document.getElementById('targetHRVal').innerText = Math.round(targetHR); resultsDiv.style.display = 'block'; }

Understanding the Heart Rate Reserve (HRR) Calculation

The Heart Rate Reserve (HRR) is the difference between your measured or predicted maximum heart rate and your resting heart rate. Unlike calculating intensity based solely on your maximum heart rate, HRR provides a more personalized metric because it accounts for your baseline level of fitness through your resting pulse.

The Heart Rate Reserve Formula

To find your HRR, the math is straightforward:

HRR = Max Heart Rate – Resting Heart Rate

The Karvonen Formula

The most common application of HRR is in the Karvonen Formula. This method is used by athletes and fitness professionals to determine target heart rate zones for specific training intensities. By factoring in the reserve, the zones are tailored to the individual's cardiovascular capacity.

Target HR = (Heart Rate Reserve × Training Intensity%) + Resting Heart Rate

Example Calculation

Let's look at a practical example for a 40-year-old individual who wants to train at 60% intensity:

  • Step 1: Estimate Max HR: 220 – 40 = 180 BPM
  • Step 2: Measure Resting HR: Assume 70 BPM
  • Step 3: Calculate HRR: 180 – 70 = 110 BPM
  • Step 4: Calculate Target HR: (110 × 0.60) + 70 = 136 BPM

Why Use HRR Instead of Just Max Heart Rate?

If you only use the standard percentage of Max Heart Rate (MHR), a highly fit individual with a low resting heart rate and a sedentary individual with a high resting heart rate might be given the same target zones. This can lead to overtraining or undertraining. Because HRR reflects the actual "working range" of the heart, it is considered the gold standard for aerobic exercise prescription.

Intensity Guidelines

Intensity Level % of HRR
Light (Warm-up) 30% – 40%
Moderate (Fat Burn) 40% – 60%
Vigorous (Aerobic) 60% – 90%

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