Resting Heart Rate (RHR) is a critical metric for gauging cardiovascular health, recovery status, and fitness levels. Unlike a simple spot-check of your pulse, Garmin devices utilize sophisticated algorithms and continuous optical sensor data to determine a daily RHR that is statistically significant.
Understanding how your device arrives at this number can help you interpret your health data more accurately and train more effectively.
The Garmin RHR Algorithm Explained
Garmin determines your Resting Heart Rate differently depending on whether you wear your device while you sleep or only during the day.
With Sleep Data (Preferred): If you wear your device overnight, Garmin calculates RHR based on the average heart rate measured over a specific interval (typically the lowest 1-minute or 30-minute average, depending on the model generation) while you are in a deep rest state. This is generally considered the most accurate method as external stressors are minimized.
Without Sleep Data: If you do not wear the device to bed, the algorithm looks for the lowest sustained average heart rate recorded during the day while you are awake but inactive (e.g., sitting quietly).
The calculation is not instantaneous. It requires a sustained period of low activity to ensure the reading isn't a false low caused by a sensor error or a momentary dip.
Garmin RHR Simulation & Zone Calculator
Use this calculator to simulate how Garmin processes your heart rate data to determine your RHR. By inputting your lowest observed readings, you can see which value Garmin would likely select and how that impacts your Heart Rate Zones (based on Heart Rate Reserve).
Yes
No
Calculated Garmin RHR: — bpm
Estimated Max HR (220-Age): — bpm
Heart Rate Reserve (HRR): — bpm
Impact on Heart Rate Zones (Based on HRR):
Zone
Intensity
Range (bpm)
function calculateGarminRHR() {
var ageInput = document.getElementById('age').value;
var wearSleep = document.getElementById('wearSleep').value;
var sleepHRInput = document.getElementById('sleepHR').value;
var awakeHRInput = document.getElementById('awakeHR').value;
// Validation
if (ageInput === "" || awakeHRInput === "") {
alert("Please enter your age and at least your awake heart rate.");
return;
}
var age = parseFloat(ageInput);
var sleepHR = parseFloat(sleepHRInput);
var awakeHR = parseFloat(awakeHRInput);
var finalRHR = 0;
var explanation = "";
// Garmin Logic Simulation
if (wearSleep === 'yes') {
if (isNaN(sleepHR)) {
alert("If you wore the device to sleep, please enter your sleep heart rate.");
return;
}
// Logic: Garmin prioritizes sleep data for RHR
finalRHR = sleepHR;
explanation = "Because you wore the device to sleep, Garmin uses the lowest average recorded during your sleep cycle (" + sleepHR + " bpm), which is typically lower and more accurate than awake readings.";
} else {
// Logic: Without sleep data, Garmin uses lowest awake inactive period
finalRHR = awakeHR;
explanation = "Since sleep data is unavailable, Garmin estimates RHR based on the lowest sustained period of inactivity while awake (" + awakeHR + " bpm). This may be slightly higher than your true physiological minimum.";
}
// Calculate Max HR and Reserve
var maxHR = 220 – age;
var hrr = maxHR – finalRHR;
// Display basic results
document.getElementById('rhrResult').innerHTML = finalRHR;
document.getElementById('maxHrResult').innerHTML = maxHR;
document.getElementById('hrrResult').innerHTML = hrr;
document.getElementById('algoExplanation').innerHTML = explanation;
// Calculate Karvonen Zones
// Zone 1: 50-60% of HRR + RHR
// Zone 2: 60-70%
// Zone 3: 70-80%
// Zone 4: 80-90%
// Zone 5: 90-100%
var z1Min = Math.round((hrr * 0.50) + finalRHR);
var z1Max = Math.round((hrr * 0.60) + finalRHR);
var z2Min = z1Max + 1;
var z2Max = Math.round((hrr * 0.70) + finalRHR);
var z3Min = z2Max + 1;
var z3Max = Math.round((hrr * 0.80) + finalRHR);
var z4Min = z3Max + 1;
var z4Max = Math.round((hrr * 0.90) + finalRHR);
var z5Min = z4Max + 1;
var z5Max = maxHR;
var tableHtml = `
1
Warm Up
${z1Min} – ${z1Max}
2
Easy
${z2Min} – ${z2Max}
3
Aerobic
${z3Min} – ${z3Max}
4
Threshold
${z4Min} – ${z4Max}
5
Maximum
${z5Min} – ${z5Max}
`;
document.getElementById('zoneTableBody').innerHTML = tableHtml;
// Show result box
document.getElementById('result').style.display = 'block';
}
Factors That Influence Garmin's RHR Calculation
Even with the same device, your calculated RHR can fluctuate due to several variables. Understanding these can help you troubleshoot inconsistent readings.
1. Sensor Fit and Position
The Elevate™ optical heart rate sensor on the back of your watch requires direct contact with the skin. If the watch is too loose, light can leak in, causing inaccurate spikes or drops. If it is too tight, it may restrict blood flow, altering the reading.
2. Consumption of Stimulants
Caffeine, alcohol, and late-night meals can keep your heart rate elevated during sleep. If you consume alcohol before bed, your "Sleep RHR" calculated by Garmin will likely be higher than normal, reflecting the body's effort to metabolize the alcohol.
3. Training Load
Overtraining often manifests as an elevated Resting Heart Rate. Garmin uses your 7-day average RHR trends to determine your "Body Battery" and recovery status. A sudden consistent rise in RHR is often a flag used by the Firstbeat Analytics engine to suggest rest.
Why Is My Garmin RHR Higher Than My Manual Count?
Users often notice a discrepancy between taking their pulse manually for 15 seconds and the number on their watch. This occurs because:
Sampling Rate: Garmin averages data over a specific duration (often 1 minute) to smooth out signal noise, whereas a manual count is a snapshot.
Lowest vs. Current: The RHR displayed in your Garmin Connect app is the lowest average found in the last 24 hours (or sleep cycle), not necessarily your heart rate right now.
Sleep vs. Awake: As demonstrated in the calculator above, if you wear the watch to sleep, your RHR will almost always be lower than if you only wear it during the day, as your metabolism drops significantly during deep sleep.