Tip: Measure this in the morning before getting out of bed.
Your Personalized Zones
Maximum Heart Rate (MHR):— bpm
Heart Rate Reserve:— bpm
🔥 Fat Burning Zone (60% – 70%)
— to — BPM
Best intensity for oxidizing fat as primary fuel.
❤️ Aerobic/Cardio Zone (70% – 80%)
— to — BPM
Best for cardiovascular endurance and calorie burning.
function calculateZones() {
// 1. Get input values
var ageInput = document.getElementById('thr_age');
var rhrInput = document.getElementById('thr_rhr');
var errorDiv = document.getElementById('error_display');
var resultDiv = document.getElementById('results_display');
var age = parseFloat(ageInput.value);
var rhr = parseFloat(rhrInput.value);
// 2. Validation
if (isNaN(age) || age 110) {
errorDiv.style.display = 'block';
errorDiv.innerHTML = "Please enter a valid age between 10 and 110.";
resultDiv.style.display = 'none';
return;
}
if (isNaN(rhr) || rhr 200) {
errorDiv.style.display = 'block';
errorDiv.innerHTML = "Please enter a valid resting heart rate (usually between 40-100 BPM).";
resultDiv.style.display = 'none';
return;
}
// Hide error if inputs are valid
errorDiv.style.display = 'none';
// 3. Calculation Logic (Karvonen Formula)
// MHR = 220 – Age
var maxHeartRate = 220 – age;
// Heart Rate Reserve (HRR) = MHR – Resting Heart Rate
var heartRateReserve = maxHeartRate – rhr;
// Fat Burn Zone: 60% to 70% intensity
// Formula: (HRR * %) + RHR
var fatBurnLow = Math.round((heartRateReserve * 0.60) + rhr);
var fatBurnHigh = Math.round((heartRateReserve * 0.70) + rhr);
// Cardio Zone: 70% to 80% intensity
var cardioLow = Math.round((heartRateReserve * 0.70) + rhr);
var cardioHigh = Math.round((heartRateReserve * 0.80) + rhr);
// 4. Update UI
document.getElementById('display_mhr').innerHTML = maxHeartRate + " bpm";
document.getElementById('display_hrr').innerHTML = heartRateReserve + " bpm";
document.getElementById('fat_burn_low').innerHTML = fatBurnLow;
document.getElementById('fat_burn_high').innerHTML = fatBurnHigh;
document.getElementById('cardio_low').innerHTML = cardioLow;
document.getElementById('cardio_high').innerHTML = cardioHigh;
// Show results
resultDiv.style.display = 'block';
}
Understanding Your Target Heart Rate for Weight Loss
When exercising to lose weight, intensity matters. While simply moving your body burns calories, training within specific heart rate zones can optimize your body's ability to burn fat as fuel. This calculator uses the Karvonen Formula, which is considered more accurate than standard calculations because it accounts for your Resting Heart Rate (RHR), essentially tailoring the results to your current fitness level.
What is the "Fat Burning Zone"?
The "Fat Burning Zone" typically corresponds to a moderate exercise intensity, roughly 60% to 70% of your maximum heart rate reserve. In this zone, the body relies more heavily on stored fat for energy compared to glycogen (carbohydrates).
Low Intensity (Below 60%): Good for recovery, but burns fewer total calories.
Moderate Intensity (60-70% – Fat Burn): The "sweet spot" where a higher percentage of calories burned comes from fat. It is sustainable for longer durations.
Vigorous Intensity (70-80% – Cardio): Burns more total calories per minute, but a lower percentage comes from fat. However, the "afterburn" effect (EPOC) is higher.
How to Measure Resting Heart Rate (RHR)
For the most accurate results from this calculator, you need to know your true Resting Heart Rate. Here is how to measure it:
Best Time: Check it immediately after waking up in the morning, before you sit up or get out of bed.
Technique: Place your index and middle fingers on your wrist (radial artery) or the side of your neck (carotid artery).
Count: Count the beats for 30 seconds and multiply by 2 to get your Beats Per Minute (BPM).
Average: For best accuracy, take the measurement over 3 consecutive mornings and calculate the average.
Why Use the Karvonen Formula?
The standard "220 minus age" formula assumes everyone of the same age has the same fitness level. The Karvonen formula includes your resting heart rate in the math. A lower resting heart rate usually indicates better cardiovascular fitness. By factoring this in, the calculator ensures your target zones are not too easy (if you are fit) or too hard (if you are just starting out).
Using These Numbers Effectively
To maximize weight loss:
Warm Up: Spend 5-10 minutes gradually increasing your heart rate.
Stay in Zone: Aim to keep your heart rate between the "Fat Burn Low" and "Fat Burn High" numbers calculated above for at least 30-45 minutes per session.
Monitor: Use a smartwatch, chest strap, or take your pulse periodically during exercise to ensure you aren't pushing too hard or slacking off.
Mix it Up: While the fat burning zone is great, incorporating 1-2 days of higher intensity cardio (the Aerobic Zone) can improve overall heart health and metabolism.
Disclaimer: This calculator is for informational purposes only. Always consult with a physician before starting a new exercise program, especially if you have pre-existing heart conditions or have been sedentary.