Heart Rate Reserve is Calculated by

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Heart Rate Reserve (HRR) & Target Heart Rate Calculator

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

Your Results:

function calculateHRR() { var age = parseFloat(document.getElementById('age').value); var rhr = parseFloat(document.getElementById('rhr').value); var intensity = parseFloat(document.getElementById('intensity').value); var resultBox = document.getElementById('hrr-result-box'); var resultDiv = document.getElementById('hrr-result'); if (isNaN(age) || isNaN(rhr) || isNaN(intensity) || age <= 0 || rhr <= 0) { resultBox.style.display = "block"; resultDiv.innerHTML = "Please enter valid positive numbers for all fields."; return; } // Formulas // Max Heart Rate (MHR) = 220 – Age // Heart Rate Reserve (HRR) = MHR – Resting Heart Rate (RHR) // Target Heart Rate (THR) = (HRR * Intensity%) + RHR var mhr = 220 – age; var hrr = mhr – rhr; var thr = (hrr * (intensity / 100)) + rhr; if (hrr <= 0) { resultBox.style.display = "block"; resultDiv.innerHTML = "Calculated Max Heart Rate is lower than Resting Heart Rate. Please check your inputs."; return; } resultBox.style.display = "block"; var output = "Max Heart Rate (MHR): " + Math.round(mhr) + " beats per minute (bpm)"; output += "Heart Rate Reserve (HRR): " + Math.round(hrr) + " bpm"; output += "Target Heart Rate (" + intensity + "% Intensity): " + Math.round(thr) + " bpm"; output += "Your Heart Rate Reserve (HRR) represents the cushion between your resting heart rate and your maximum heart rate. It is a key metric for determining training zones using the Karvonen formula."; resultDiv.innerHTML = output; }

How Heart Rate Reserve is Calculated

Heart Rate Reserve (HRR) is a vital metric used by fitness professionals and athletes to tailor workout intensity to an individual's specific physiology. Unlike simple percentages of Maximum Heart Rate, HRR takes your cardiovascular fitness level into account by including your Resting Heart Rate (RHR).

The Step-by-Step HRR Formula

Heart rate reserve is calculated by subtracting your resting heart rate from your maximum heart rate. The process follows these three steps:

  1. Estimate Maximum Heart Rate (MHR): The most common formula is 220 - Age.
  2. Measure Resting Heart Rate (RHR): This is best measured first thing in the morning while you are still lying in bed.
  3. The Subtraction: HRR = MHR - RHR.

Calculating Target Heart Rate (The Karvonen Formula)

Once you know how heart rate reserve is calculated, you can find your Target Heart Rate (THR) for specific exercise zones. This is known as the Karvonen Formula:

Target Heart Rate = (HRR × Intensity%) + RHR

For example, if a 40-year-old has a resting heart rate of 60 bpm and wants to exercise at 70% intensity:

  • MHR: 220 – 40 = 180 bpm
  • HRR: 180 – 60 = 120 bpm
  • THR: (120 × 0.70) + 60 = 144 bpm

Why Use HRR Instead of Max HR?

Using only a percentage of Maximum Heart Rate can be inaccurate because it ignores a person's baseline fitness. Two 30-year-olds may have the same MHR (190 bpm), but if one has a resting heart rate of 50 (very fit) and the other has a resting heart rate of 80 (sedentary), their Heart Rate Reserves are significantly different (140 vs 110). Using HRR ensures that the "fit" person is working hard enough and the "sedentary" person is not over-exerting themselves.

Training Zones Based on Intensity

  • Recovery/Light: 40% – 50% of HRR. Used for warm-ups and active recovery.
  • Moderate (Aerobic): 50% – 70% of HRR. Ideal for building endurance and burning fat.
  • Vigorous (Anaerobic): 70% – 85% of HRR. Used to improve cardiovascular capacity and speed.
  • Maximum Effort: > 85% of HRR. High-intensity interval training (HIIT) and sprinting.

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