How to Calculate Heart Rate Reserve Percentage

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Heart Rate Reserve (HRR) Calculator

Determine your target heart rate zones using the Karvonen Formula.

Your Results

Estimated Max Heart Rate: BPM

Heart Rate Reserve (HRR): BPM

Target Training Heart Rate

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; } // Calculations // 1. Estimate Max Heart Rate (Haskell & Fox formula) var maxHR = 220 – age; // 2. Heart Rate Reserve var hrr = maxHR – restingHR; // 3. Karvonen Formula: Target Heart Rate = [(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) + " BPM"; resultArea.style.display = 'block'; }

How to Calculate Heart Rate Reserve (HRR) Percentage

Calculating your Heart Rate Reserve (HRR) is one of the most effective ways to tailor your cardiovascular training to your specific fitness level. Unlike simple "Max Heart Rate" calculations, the HRR method (often called the Karvonen Formula) accounts for your resting heart rate, which is a key indicator of your current aerobic health.

The Formula: How it Works

The Heart Rate Reserve is the difference between your maximum heart rate and your resting heart rate. This "reserve" represents the range of heartbeats available for exertion. To calculate a specific percentage of that reserve, we use the following formula:

Step 1: 220 – Age = Estimated Max HR
Step 2: Max HR – Resting HR = Heart Rate Reserve (HRR)
Step 3: (HRR × Intensity %) + Resting HR = Target Heart Rate

Practical Example

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

  • Max HR: 220 – 40 = 180 BPM
  • HRR: 180 – 70 = 110 BPM
  • Target Heart Rate: (110 × 0.60) + 70 = 136 BPM

In this example, to reach 60% of their heart rate reserve, the individual should aim for a pulse of approximately 136 beats per minute during exercise.

Why Use Heart Rate Reserve Instead of Max HR?

Simple Max Heart Rate percentages (e.g., 70% of 220-age) don't account for how fit you are at rest. Two people of the same age might have vastly different resting heart rates (one at 50 BPM and one at 80 BPM). Using HRR ensures that the intensity is relative to the individual's "working range," making the workout safer and more effective for building endurance.

How to Measure Your Resting Heart Rate

For the most accurate calculation, you need an accurate Resting Heart Rate (RHR). The best time to measure this is immediately after waking up, before you get out of bed or consume caffeine. Place two fingers on your radial pulse (wrist) or carotid pulse (neck) and count the beats for 60 seconds. Repeat this for three mornings and take the average for the most precise data.

Target Intensity Zones

Depending on your fitness goals, you may want to target different HRR percentages:

  • 50% – 60%: Light intensity, ideal for warm-ups and recovery.
  • 60% – 70%: Moderate intensity, great for fat metabolism and basic endurance.
  • 70% – 85%: Vigorous intensity, improves aerobic capacity and VO2 Max.

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