Tip: Measure your pulse for 60 seconds while lying in bed in the morning.
Estimated Maximum Heart Rate:0 BPM
Heart Rate Reserve (HRR):0 BPM
Your Fat Burning Zone: 0 – 0 BPM
(60% – 70% intensity level)
function calculateFatBurnZone() {
// Get inputs
var ageInput = document.getElementById('inputAge');
var rhrInput = document.getElementById('inputRHR');
var resultContainer = document.getElementById('resultContainer');
var displayMaxHR = document.getElementById('displayMaxHR');
var displayHRR = document.getElementById('displayHRR');
var displayZone = document.getElementById('displayZone');
// Parse values
var age = parseFloat(ageInput.value);
var rhr = parseFloat(rhrInput.value);
// Validation
if (isNaN(age) || age 110) {
alert("Please enter a valid age between 10 and 110.");
return;
}
if (isNaN(rhr) || rhr 200) {
alert("Please enter a valid resting heart rate (typically between 40 and 100).");
return;
}
// Calculations using Karvonen Formula
// 1. Calculate Maximum Heart Rate (MHR) = 220 – Age
var maxHR = 220 – age;
// 2. Calculate Heart Rate Reserve (HRR) = MHR – Resting HR
var hrr = maxHR – rhr;
// 3. Calculate Fat Burning Zone (typically 60% to 70% intensity)
// Lower Bound = (HRR * 0.60) + Resting HR
var lowerBound = Math.round((hrr * 0.60) + rhr);
// Upper Bound = (HRR * 0.70) + Resting HR
var upperBound = Math.round((hrr * 0.70) + rhr);
// Update UI
displayMaxHR.innerHTML = maxHR + " BPM";
displayHRR.innerHTML = hrr + " BPM";
displayZone.innerHTML = lowerBound + " – " + upperBound + " BPM";
// Show results
resultContainer.style.display = "block";
}
How to Calculate Your Fat Burning Zone
Understanding your heart rate is crucial for optimizing cardiovascular workouts, specifically when your goal is to burn fat. While intense cardio improves endurance, operating within a specific intensity "zone" encourages your body to utilize stored fat as its primary fuel source.
The Science Behind the Fat Burning Zone
The "fat burning zone" is typically defined as working out at 60% to 70% of your heart rate reserve. At this lower intensity, your body has sufficient oxygen available to oxidize fat for energy. Higher intensities (anaerobic zones) force the body to switch to glycogen (carbohydrates) for immediate fuel because it's faster to process.
The Karvonen Formula
While the generic formula ($220 – \text{Age}$) provides a rough estimate of maximum heart rate, it fails to account for individual fitness levels. This calculator uses the Karvonen Formula, widely regarded by exercise physiologists as the most accurate method for determining target zones because it incorporates your Resting Heart Rate (RHR).
By factoring in your RHR, the calculation adjusts for your cardiovascular health. A fitter individual typically has a lower resting heart rate, which changes their heart rate reserve calculations significantly compared to the standard method.
How to Measure Resting Heart Rate
To get the most accurate result from this calculator, you need a precise Resting Heart Rate measurement:
Timing: The best time to measure is immediately after waking up in the morning, before you get out of bed or drink coffee.
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 a full 60 seconds, or count for 30 seconds and multiply by 2.
Average: For best results, take the measurement over three consecutive mornings and calculate the average.
Applying the Results
Once you have your target range (e.g., 125 – 135 BPM):
Duration Matters: Fat oxidation takes time to ramp up. Aim for sustained activities (walking, jogging, cycling) lasting 30 to 60 minutes.
Monitor Consistently: Use a smartwatch, fitness tracker, or chest strap monitor to ensure you stay within the calculated Lower and Upper bounds.
Don't Ignore HIIT: While the fat burning zone burns a higher percentage of calories from fat, High-Intensity Interval Training (HIIT) burns more total calories in less time. A balanced routine often includes both.
Example Calculation
Let's look at a 40-year-old individual with a resting heart rate of 70 BPM: