Understanding how Whoop calculates Resting Heart Rate (RHR) requires looking beyond simple averages. Unlike many fitness trackers that take readings throughout the day or calculate a mean average of your entire sleep duration, Whoop uses a specific, dynamic weighting system focused on Slow Wave Sleep (SWS).
This calculator simulates the difference between a "Standard Whole-Night Average" (used by generic trackers) and the "SWS-Weighted Method" utilized by Whoop to determine your recovery baseline.
Estimate Your RHR Baseline
The average heart rate during your deepest sleep stage (Slow Wave Sleep). Whoop prioritizes this.
Heart rate during light sleep stages (usually higher than deep sleep).
Heart rate during Rapid Eye Movement (often volatile and higher).
Heart rate spikes caused by tossing, turning, or brief wakeups.
Standard Tracker Average (Whole Night):— BPM
Whoop-Style RHR (SWS Weighted):— BPM
Enter data to see the analysis.
The Science: Why Whoop Targets Slow Wave Sleep
Whoop calculates Resting Heart Rate (RHR) specifically during the last episode of Slow Wave Sleep (SWS) each night. This is distinct from other methods for several reasons:
Consistency: SWS is the stage of sleep where your body is most physically restored and external noise (movement, mental activity) is minimized.
Parasympathetic Dominance: During deep sleep, the parasympathetic nervous system (rest and digest) is most active, providing the "truest" baseline of your cardiac health.
Artifact Filtering: By isolating SWS, the algorithm filters out heart rate spikes caused by REM dreaming or restlessness, which can artificially inflate RHR readings on other devices.
How the Calculation Works
While the exact proprietary algorithm is complex, the core logic follows these steps:
Detection: The strap identifies sleep stages using accelerometer and photoplethysmography (PPG) data.
Isolation: It pinpoints periods of Deep Sleep (SWS).
Dynamic Weighting: It calculates a weighted average, giving significantly more weight to the lowest consistent readings found in SWS and discarding "noise" (spikes from movement).
Why Lower Isn't Always "Better"
While a lower RHR generally indicates better cardiovascular fitness, the Whoop methodology focuses on consistency relative to your own baseline. A sudden drop in RHR can sometimes indicate different physiological issues, just as a spike indicates strain or illness. Because Whoop measures RHR at the most consistent time (SWS), deviations from your baseline are more statistically significant indicators of recovery status than random daytime measurements.
function calculateWhoopRHR() {
// Get input values
var sws = document.getElementById('swsHR').value;
var light = document.getElementById('lightHR').value;
var rem = document.getElementById('remHR').value;
var spikes = document.getElementById('artifacts').value;
// Validate inputs
if (sws === "" || light === "" || rem === "" || spikes === "") {
alert("Please fill in all heart rate fields to calculate the comparison.");
return;
}
// Parse to floats
var swsVal = parseFloat(sws);
var lightVal = parseFloat(light);
var remVal = parseFloat(rem);
var spikesVal = parseFloat(spikes);
// Sanity Check
if (swsVal <= 0 || lightVal <= 0 || remVal <= 0 || spikesVal 0) {
noteDisplay.innerHTML = "Analysis: The Standard method is " + diff + " BPM higher than the Whoop estimate. This is because generic trackers include REM sleep and movement spikes in their average. Whoop isolates the Deep Sleep phase (SWS), providing a lower, more consistent baseline that better reflects your recovery.";
} else {
noteDisplay.innerHTML = "Analysis: Your sleep stages have very similar Heart Rates. Typically, Whoop yields a lower RHR by filtering out REM and movement spikes, but in your simulated data, the variance is low.";
}
}