Workout Heart Rate Zones Calculator

Workout Heart Rate Zones Calculator

Determine your optimal training intensity zones using the Karvonen formula, which accounts for your resting heart rate for greater accuracy.

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Best measured right after waking up, before getting out of bed.

Please enter valid age and resting heart rate values.

function calculateHeartRateZones() { var ageInput = document.getElementById("hrInputAge").value; var rhrInput = document.getElementById("hrInputRHR").value; var resultDiv = document.getElementById("hrzResult"); var errorDiv = document.getElementById("hrError"); var age = parseFloat(ageInput); var rhr = parseFloat(rhrInput); if (isNaN(age) || age <= 0 || isNaN(rhr) || rhr 120 || rhr > 200) { errorDiv.style.display = "block"; resultDiv.style.display = "none"; return; } errorDiv.style.display = "none"; // 1. Calculate Estimated Maximum Heart Rate (MHR) using standard 220 – age var mhr = 220 – age; // Check if RHR is higher than MHR (invalid state) if (rhr >= mhr) { errorDiv.innerHTML = "Resting Heart Rate cannot be higher than estimated Max Heart Rate (" + mhr + " bpm)."; errorDiv.style.display = "block"; resultDiv.style.display = "none"; return; } // 2. Calculate Heart Rate Reserve (HRR) – Karvonen Method foundation var hrr = mhr – rhr; // Helper function for Karvonen formula: (HRR * intensity%) + RHR function calculateKarvonen(intensityDecimal) { return Math.round((hrr * intensityDecimal) + rhr); } // Calculate zone boundaries var z1_low = calculateKarvonen(0.50); var z1_high = calculateKarvonen(0.60) – 1; // Subtract 1 to avoid overlap with next zone start var z2_low = calculateKarvonen(0.60); var z2_high = calculateKarvonen(0.70) – 1; var z3_low = calculateKarvonen(0.70); var z3_high = calculateKarvonen(0.80) – 1; var z4_low = calculateKarvonen(0.80); var z4_high = calculateKarvonen(0.90) – 1; var z5_low = calculateKarvonen(0.90); var z5_high = mhr; var htmlOutput = '

'; htmlOutput += 'Estimated Max Heart Rate (MHR): ' + mhr + ' bpm'; htmlOutput += 'Heart Rate Reserve (HRR): ' + hrr + ' bpm'; htmlOutput += '

'; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += ''; htmlOutput += '

Zone	Intensity	Target Range (bpm)
Zone 1Very Light	50% – 60%	' + z1_low + ' – ' + z1_high + ' bpm
Zone 2Light	60% – 70%	' + z2_low + ' – ' + z2_high + ' bpm
Zone 3Moderate	70% – 80%	' + z3_low + ' – ' + z3_high + ' bpm
Zone 4Hard	80% – 90%	' + z4_low + ' – ' + z4_high + ' bpm
Zone 5Maximum	90% – 100%	' + z5_low + ' – ' + z5_high + ' bpm

'; resultDiv.innerHTML = htmlOutput; resultDiv.style.display = "block"; }

Understanding Your Heart Rate Training Zones

Heart rate zone training is a systematic approach to exercise that uses your heart rate (measured in beats per minute, or bpm) as a gauge of intensity. By training in specific zones, you can target different physiological adaptations, from improving endurance and fat burning to increasing maximum performance speed.

While basic calculators use a simple percentage of your Maximum Heart Rate (MHR), this calculator utilizes the **Karvonen Formula**. This method is generally considered more accurate for individuals with varying fitness levels because it incorporates your **Resting Heart Rate (RHR)**. By factoring in your RHR, the calculation determines your "Heart Rate Reserve"—the actual usable range between your resting baseline and your maximum effort.

How the Calculations Work

1. Maximum Heart Rate (MHR): Estimated using the standard formula: 220 - Age. For example, a 40-year-old has an estimated MHR of 180 bpm.
2. Heart Rate Reserve (HRR): The difference between your maximum and resting rates: MHR - RHR. If that 40-year-old has a resting heart rate of 60 bpm, their HRR is 120 bpm (180 – 60).
3. Target Zone Calculation: The Karvonen formula is: (HRR × Intensity Percentage) + RHR.

The 5 Training Zones Explained

• Zone 1 (Very Light, 50-60%): Used for warm-ups, cool-downs, and active recovery. It aids in blood flow and recovery without straining the body.
• Zone 2 (Light, 60-70%): Often called the "fat-burning zone." This is the primary zone for building a solid aerobic base. You should be able to hold a conversation easily here.
• Zone 3 (Moderate, 70-80%): Sometimes referred to as "tempo" or the "grey zone." It improves aerobic capacity and blood circulation but can be fatiguing if sustained too long. Breathing becomes heavier.
• Zone 4 (Hard, 80-90%): This is your lactate threshold zone. Training here helps your body get better at dealing with the lactic acid produced during high-intensity effort. Sustainability is limited.
• Zone 5 (Maximum, 90-100%): Your peak effort zone, used for very short intervals or final sprints. It taxes your anaerobic system and neuromuscular pathways.

To get the most accurate results, ensure your Resting Heart Rate input is correct. The best time to measure it is immediately upon waking up, while still lying in bed calmly, before checking your phone or drinking coffee.