Garmin watches are quite accurate for resting heart rate, typically landing within about 1 beat per minute of a medical-grade ECG reading when you’re sitting still. That’s close enough to reliably track trends over time, which is the main reason most people check this number. The accuracy drops during intense exercise, but at rest, the optical sensor on your wrist performs well.
How Garmin Calculates Resting Heart Rate
Garmin defines your daily resting heart rate as the lowest 30-minute average recorded in a 24-hour period. In practice, this almost always falls during your deepest sleep, when your body is most relaxed and your heart rate naturally dips to its lowest point.
This is worth understanding because it explains a common source of confusion. If you switch from a Garmin to an Apple Watch (or vice versa), you’ll likely see different resting heart rate numbers, and it doesn’t mean one device is broken. Apple weights its resting heart rate calculation heavily toward the period right after you wake up and explicitly excludes readings taken while you’re asleep. Garmin pulls from any point in the 24-hour window, including deep sleep. Since your heart rate during deep sleep is lower than right after waking, Garmin’s number will often read a few beats lower. Both approaches are valid, just measuring slightly different things.
What the Research Shows
A 2025 study published in Frontiers in Digital Health compared Garmin’s optical sensor against a clinical ECG across multiple conditions. At rest, the average difference was just 0.67 beats per minute, with the ECG reading slightly higher. That’s a negligible gap for everyday health tracking.
During exercise, the story changes. When heart rate ramps up quickly (like interval training or hill sprints), the difference between the Garmin and ECG jumped to around 3 to 11 beats per minute depending on the phase. The sensor struggles most during rapid transitions in intensity, not during steady-state activity. But for resting heart rate specifically, the data is reassuring.
One important caveat from the same study: the limits of agreement (the range where 95% of readings fell) exceeded plus or minus 5 beats per minute across all tasks, including rest. That means on any single reading, your Garmin could be off by several beats. The accuracy improves dramatically when you look at averages over time, which is exactly what Garmin’s 30-minute averaging method is designed to do.
Skin Tone and Sensor Reliability
Garmin watches use green LED light that bounces off blood vessels beneath your skin to detect your pulse. Because darker skin absorbs more light, there’s been concern that accuracy could suffer for people with more melanin. The physics makes this plausible: less light returning to the sensor means a weaker signal to interpret.
Research on this question is still limited. A pilot study testing wrist-based optical sensors across light, intermediate, and dark skin tones found no meaningful difference in accuracy. The average error was under 1.3 beats per minute for all skin tone groups, and there was no interaction between skin tone and exercise intensity. However, the researchers noted that their sample was small (only seven participants) and called for larger studies. A separate, larger analysis did find a moderate correlation between darker skin and reduced accuracy during high-intensity ramp phases, though the effect was specific to rapid heart rate changes rather than resting measurements.
What Affects Your Reading
The biggest factor in getting a reliable resting heart rate from your Garmin isn’t the sensor itself. It’s how you wear the watch. Garmin’s own guidance recommends wearing the watch snug enough that your skin moves with the device, but not so tight that it restricts blood flow. A loose fit creates a gap between the sensor and your skin, letting ambient light leak in and contaminate the reading. Position matters too: the watch should sit above the wrist bone, on the outer side of your wrist.
Other things that can throw off readings include:
- Tattoos under the sensor. Dark ink absorbs the green light, weakening the signal significantly. Some people with wrist tattoos find the sensor essentially stops working on that arm.
- Cold temperatures. When your hands are cold, blood vessels in your wrist constrict, reducing blood flow near the surface where the sensor reads.
- Wearing the watch too low. The tendons and bones right at the wrist joint create an uneven surface that prevents consistent skin contact.
If you wear the watch properly and consistently, your resting heart rate trend line over weeks and months will be highly reliable, even if any individual day’s reading is slightly off.
Trends Matter More Than Single Readings
The real value of Garmin’s resting heart rate tracking isn’t any one number. It’s the pattern over time. A gradual decline in resting heart rate over months typically reflects improving cardiovascular fitness. A sudden spike of 5 to 10 beats above your baseline can signal that your body is fighting an illness, under unusual stress, or not recovering well from training.
Because Garmin uses a consistent methodology (lowest 30-minute average, measured the same way every night), even if the absolute number is off by a beat or two compared to a clinical reading, the relative changes from day to day are meaningful and trackable. This is where consumer wearables genuinely shine: not as diagnostic tools, but as long-term trend monitors that can alert you to changes before you feel them.
For that purpose, Garmin’s resting heart rate is accurate enough to trust.