Apple Watch’s heart rate monitor measures 10 major metrics of heart health. But do we know how accurate the underlying heart rate sensor is?
Here’s what the data shows:
Accuracy of Apple Watch heart rate monitor in various settings. Source: 2024 Apple study.
While sedentary, Apple Watch’s heart rate monitor is accurate to within 5bpm about 98% of the time. During exercise, about 87% of measurements are within 5bpm. 95% of measurements are within 10bpm of the ground truth during exercise.
These numbers are based on Apple’s own analysis, involving tens of thousands of sessions comparing the watch itself to a gold standard in a custom-built academic lab. But you don’t need to take the manufacturer’s word for it.
Accuracy of Apple Watch heart rate monitor from academic studies
You might reasonably ask: have third party researchers, unaffiliated with Apple, validated the accuracy of the Apple Watch’s heart rate monitor? Several studies have been published.
Accuracy of Apple Watch heart rate monitor vs Garmin, Fitbit, and Polar. Source: European Journal of Sports Science, 2023.
The Apple Watch’s heart rate monitor was accurate to within 2.3 bpm in a 2023 study of 60 healthy participants. Among patients with cardiovascular disease, a 2019 study found an average error of 6-7 bpm. Earlier studies on the Apple Watch Series 4, which used the second generation of sensors, found higher error. A 2019 study found a correlation of 70%.
How Apple Watch’s heart rate sensor works
Apple Watch’s optical heart rate sensor uses an array of photodiodes to shine light through your skin. There are three wavelengths of light used: green (525 nm), infrared (850-940 nm), and red (660 nm). The green and infrared light are used to measure your pulse, and the red light is used to measure your blood oxygen saturation.
Three generations of Apple Watch’s heart rate sensor
Apple has revised the optical heart rate sensor three times since 2015. The first optical heart rate sensor debuted in 2015 with the original Apple Watch. The second generation was introduced in the Series 4 (2018) and is currently used in the Apple Watch SE2. The third generation was introduced in the Series 6 (2020), alongside the oxygen sensor, and is now used in the Apple Watch Series 10 and Apple Watch Ultra 2.
| Generation | Year Introduced | Apple Watch Models | Key Features |
|---|---|---|---|
| First gen optical heart rate sensor | 2015 | Apple Watch Series 1-3, SE | Basic heart rate monitoring |
| Second gen optical heart rate sensor | 2018 | Apple Watch Series 4, 5, SE2 | Improved accuracy, lower power consumption |
| Third gen optical heart rate sensor | 2020 | Apple Watch Series 6-10, Ultra/Ultra 2 | Blood oxygen monitoring capability |
| ECG Sensor | 2018 | Apple Watch Series 4 and later | FDA-cleared Class II medical device for electrocardiogram readings |
Optical heart rate sensor vs ECG sensor
The Apple Watch has two heart rate sensors: the optical heart rate sensor and the ECG sensor. The optical sensor uses light to measure your heart rate, whereas the ECG measures the electrical signals generated by your heart. A doctor can use the ECG to diagnose heart rhythm disorders, like atrial fibrillation, atrial flutter, supraventricular tachycardia, and more.
Bottom line
In general, if you’re using the latest generation of Apple Watch’s heart rate monitor (Apple Watch Series 6 and later or Ultra 1 or later), it’s accurate.
