Simulate how Whoop determines your baseline and adjusted Max Heart Rate.
Enter the highest accurate HR you have seen during intense exercise.
Calculation Results
Standard Formula (Fox) Estimate:— BPM
Tanaka Formula (Athletic) Estimate:— BPM
Likely Whoop Max HR:— BPM
Zone 5 Threshold (90%):— BPM
function calculateWhoopMHR() {
var ageInput = document.getElementById('userAge').value;
var observedInput = document.getElementById('observedHR').value;
var resultsDiv = document.getElementById('resultsArea');
var foxDisplay = document.getElementById('foxResult');
var tanakaDisplay = document.getElementById('tanakaResult');
var whoopDisplay = document.getElementById('whoopResult');
var zone5Display = document.getElementById('zone5Result');
var messageDiv = document.getElementById('adjustmentMessage');
// Validation
if (!ageInput || isNaN(ageInput)) {
alert("Please enter a valid age.");
return;
}
var age = parseFloat(ageInput);
var observedHR = parseFloat(observedInput);
if (isNaN(observedHR)) {
observedHR = 0;
}
// 1. Calculate Standard Formulas
// Fox Formula: 220 – Age (Common baseline)
var foxMHR = 220 – age;
// Tanaka Formula: 208 – (0.7 * Age) (Often more accurate for active individuals)
var tanakaMHR = Math.round(208 – (0.7 * age));
// 2. Determine Whoop Logic
// Whoop typically uses a demographic formula initially (often closer to Tanaka or Gellish for fit users),
// but the CRITICAL logic is that it updates if Observed > Formula.
// For this calculator, we will use Tanaka as the "Smart Estimate" baseline.
var calculatedBase = tanakaMHR;
var finalWhoopMHR = calculatedBase;
var adjusted = false;
if (observedHR > calculatedBase) {
finalWhoopMHR = observedHR;
adjusted = true;
}
// 3. Calculate Zone 5 (90% of Max)
var zone5 = Math.round(finalWhoopMHR * 0.90);
// 4. Update UI
foxDisplay.innerHTML = foxMHR + " BPM";
tanakaDisplay.innerHTML = tanakaMHR + " BPM";
whoopDisplay.innerHTML = finalWhoopMHR + " BPM";
zone5Display.innerHTML = zone5 + " BPM";
if (adjusted) {
messageDiv.innerHTML = "Note: Since your observed heart rate (" + observedHR + " BPM) is higher than the demographic formula estimate (" + calculatedBase + " BPM), Whoop would likely adjust your Max HR setting to match your observed peak.";
} else {
messageDiv.innerHTML = "Note: This is based on an athletic age-based formula. If you perform a high-strain activity and reach a heart rate higher than " + finalWhoopMHR + " BPM, Whoop will automatically update this number upwards.";
}
resultsDiv.style.display = 'block';
}
Understanding How Whoop Calculates Max Heart Rate
Your Maximum Heart Rate (Max HR) is a foundational metric for the Whoop strap. It defines your heart rate zones, calculates your daily Strain, and influences how the device interprets your cardiovascular load. If your Max HR is set incorrectly, your Strain scores will be inaccurate, leading to poor recovery advice.
The Initial Calculation: Age-Based Formulas
When you first onboard with Whoop, the device does not yet have data on your physical capabilities. To establish a baseline, it utilizes a demographic formula based primarily on your age and gender. While the classic formula known as the Fox equation (220 minus age) is the most famous, modern fitness devices often utilize the Tanaka formula (208 minus 0.7 × age) or the Gellish formula, which tend to be more accurate for healthy adults.
For example, a 30-year-old would have a Max HR of 190 BPM under the Fox formula, but approximately 187 BPM under the Tanaka formula. This baseline is just a starting point.
The Adaptive Logic: "Observed" Max HR
The distinct feature of Whoop's algorithm is that it is adaptive. The calculator above simulates this logic.
Whoop continuously monitors your heart rate data during activities. If you perform a high-intensity workout—such as a sprint interval or a VO2 max test—and your heart rate sensor reliably records a value higher than your current estimated Max HR, Whoop will automatically update your Max HR to this new, higher number.
This ensures that the device is calibrated to your specific physiology rather than a generic statistical average. However, Whoop generally does not automatically lower your Max HR if you never hit the peak; it assumes you just haven't pushed that hard recently.
Why Accurate Max HR Matters for Strain
Whoop calculates "Strain" based on how much time you spend in various heart rate zones. These zones are percentages of your Max HR:
Zone 1 (Recovery): 50-60% of Max HR
Zone 2 (Fat Burn): 60-70% of Max HR
Zone 3 (Aerobic): 70-80% of Max HR
Zone 4 (Anaerobic): 80-90% of Max HR
Zone 5 (Peak): 90-100% of Max HR
If your Max HR is set too low (e.g., the formula says 180, but your real max is 200), a workout at 170 BPM will look like you are near your limit (Zone 5), resulting in an artificially inflated Strain score (e.g., 18.0+). Conversely, if your Max HR is set too high, your Strain will appear lower than it actually is.
Manual Adjustments
While the automatic detection is useful, it relies on the sensor getting a clean reading. Sometimes optical heart rate sensors can experience "cadence lock" or spikes that record a falsely high heart rate. If you see a Max HR on your profile that seems impossible (e.g., 230 BPM), you can manually adjust it in the App Settings under Activity Settings > Max Heart Rate.