function calculateTHR() {
var age = document.getElementById('age').value;
var restingHR = document.getElementById('restingHR').value;
var intensity = document.getElementById('intensity').value;
var resultContainer = document.getElementById('thr-result-container');
if (!age || age 120) {
alert('Please enter a valid age.');
return;
}
if (!restingHR || restingHR 220) {
alert('Please enter a valid resting heart rate.');
return;
}
var parsedAge = parseFloat(age);
var parsedRHR = parseFloat(restingHR);
var parsedIntensity = parseFloat(intensity) / 100;
// Maximum Heart Rate (Fox Formula)
var mhr = 220 – parsedAge;
// Heart Rate Reserve (Karvonen Formula)
var hrr = mhr – parsedRHR;
// Target Heart Rate
var targetTHR = (hrr * parsedIntensity) + parsedRHR;
document.getElementById('mhr-display').innerText = Math.round(mhr);
document.getElementById('target-bpm-display').innerText = Math.round(targetTHR);
var desc = "";
if (intensity == 50) desc = "Ideal for recovery and beginning of exercise.";
if (intensity == 60) desc = "Optimizes fat metabolism and builds basic endurance.";
if (intensity == 70) desc = "Improves cardiovascular fitness and lung capacity.";
if (intensity == 80) desc = "Increases lactate threshold and high-speed endurance.";
if (intensity == 90) desc = "Peak performance training; only for short intervals.";
document.getElementById('zone-description').innerText = desc;
resultContainer.style.display = 'block';
}
How to Use the Target Heart Rate Calculator
Understanding your target heart rate (THR) is essential for optimizing your fitness routine. Whether you are looking to burn fat, improve your stamina, or prepare for a competitive race, training in the right heart rate zone ensures you are working hard enough to see results without overtraining.
What is the Karvonen Formula?
This calculator utilizes the Karvonen Formula, which is considered more accurate than simple percentage-of-max-heart-rate calculations. By including your Resting Heart Rate (RHR), it accounts for your current level of cardiovascular fitness. The formula is as follows:
- Max Heart Rate (MHR) = 220 – Age
- Heart Rate Reserve (HRR) = MHR – Resting Heart Rate
- Target Heart Rate = (HRR × Intensity%) + Resting Heart Rate
Common Heart Rate Training Zones
Depending on your goals, you should aim for different intensity percentages:
| Zone |
Intensity |
Benefit |
| Warm Up |
50-60% |
Recovery and metabolic priming. |
| Fat Burn |
60-70% |
Efficient calorie burning and endurance. |
| Aerobic |
70-80% |
Cardiovascular strengthening. |
| Anaerobic |
80-90% |
Improved performance and speed. |
Calculation Example
Consider a 40-year-old individual with a resting heart rate of 70 BPM who wants to exercise at 70% intensity (Aerobic Zone):
- Max HR: 220 – 40 = 180 BPM
- HR Reserve: 180 – 70 = 110 BPM
- Target HR: (110 × 0.70) + 70 = 77 + 70 = 147 BPM
In this case, 147 beats per minute is the target for a moderate-intensity aerobic workout.
Pro Tip: To find your Resting Heart Rate accurately, measure your pulse for 60 seconds immediately after waking up in the morning, before getting out of bed.