🔥 Fat Burning Zone (60-70%)
Best for metabolizing fat directly.
0 – 0 bpm
❤️ Aerobic / Cardio Zone (70-80%)
Best for cardiovascular endurance and high calorie burn.
0 – 0 bpm
function calculateWeightLossZone() {
// Get Inputs
var age = document.getElementById('hr_age').value;
var rhr = document.getElementById('hr_rhr').value;
// Validation
if (age === "" || rhr === "") {
alert("Please enter both your Age and your Resting Heart Rate.");
return;
}
var ageNum = parseFloat(age);
var rhrNum = parseFloat(rhr);
if (isNaN(ageNum) || isNaN(rhrNum) || ageNum < 10 || rhrNum < 30) {
alert("Please enter valid numerical values.");
return;
}
// Logic: Karvonen Formula
// 1. Calculate Max Heart Rate (MHR) = 220 – Age
var maxHR = 220 – ageNum;
// 2. Calculate Heart Rate Reserve (HRR) = MHR – RHR
var reserveHR = maxHR – rhrNum;
// 3. Calculate Target Zones
// Formula: (HRR * Intensity%) + RHR
// Fat Burn Zone (60% to 70%)
var fatLow = Math.round((reserveHR * 0.60) + rhrNum);
var fatHigh = Math.round((reserveHR * 0.70) + rhrNum);
// Cardio Zone (70% to 80%)
var cardioLow = Math.round((reserveHR * 0.70) + rhrNum) + 1; // Start +1 from previous
var cardioHigh = Math.round((reserveHR * 0.80) + rhrNum);
// Display Results
document.getElementById('res_mhr').innerHTML = maxHR;
document.getElementById('res_reserve').innerHTML = reserveHR;
document.getElementById('res_fat_low').innerHTML = fatLow;
document.getElementById('res_fat_high').innerHTML = fatHigh;
document.getElementById('res_cardio_low').innerHTML = cardioLow;
document.getElementById('res_cardio_high').innerHTML = cardioHigh;
// Show result div
document.getElementById('hr_results').style.display = 'block';
}
What Should My Heart Rate Be To Lose Weight?
Finding the optimal heart rate for weight loss is essential for maximizing the efficiency of your workouts. While exercising at any intensity burns calories, targeting specific heart rate zones can help your body prioritize burning stored fat as fuel. This calculator uses the Karvonen Formula, widely considered the gold standard for determining personal exercise intensity zones because it accounts for your Resting Heart Rate (RHR).
Understanding the Fat Burning Zone
The "Fat Burning Zone" typically occurs when your heart rate is between 60% and 70% of your heart rate reserve. In this lower-intensity zone, the body relies more heavily on fat oxidation for energy rather than glycogen (carbohydrates).
For example, a 35-year-old with a resting heart rate of 70 bpm would aim for approximately 139 to 151 beats per minute (bpm) to stay in this zone. While the total calories burned per minute are lower than high-intensity exercise, a higher percentage of those calories comes from fat.
The Aerobic (Cardio) Zone
Stepping up the intensity to 70% – 80% places you in the Aerobic Zone. Here, you burn more total calories in less time. This zone improves cardiovascular health and stamina. For pure weight loss, a mix of both zones is often recommended: long, steady-state sessions in the Fat Burning Zone and shorter, high-intensity sessions in the Aerobic Zone.
How to Use This Calculator
To get the most accurate results, follow these steps:
Determine your Age: This helps estimate your Maximum Heart Rate (MHR).
Measure your Resting Heart Rate (RHR): The best time to do this is in the morning, right after you wake up and before you get out of bed. Count your pulse for 60 seconds.
Input the Data: Enter these figures into the calculator above.
Monitor During Exercise: Use a smartwatch, fitness tracker, or chest strap to ensure you stay within the calculated ranges during your workout.
Why is the Karvonen Formula Better?
Many basic calculators simply take 220 minus your age and multiply by a percentage (e.g., MHR × 0.6). However, this ignores your fitness level. By including your Resting Heart Rate, the Karvonen method tailors the target zone to your specific cardiovascular health. As you get fitter, your RHR will likely drop, and your target zones will adjust accordingly.