Apple Claims Watch Series 12 Has Better Heart Rate Accuracy Than Any Other Wearable—But There’s a Catch.

The Apple Watch Series 12 and Ultra 4 are set to hit shelves on September 18, 2026. Apple claims the series 12 demonstrates better heart rate accuracy over competitors like Garmin and Samsung based on a study of more than 1,000 participants comparing devices.Apple will roll out a new app later this year, providing users with more health and performance insights including training readiness.Like clockwork, Apple announced that the new Apple Watch Series 12 and Ultra 4 will hit shelves on September 18. Also as expected, the company touted improvements—specifically that the Series 12 is better at detecting heart rate than other popular GPS running watches and wearables based on new research. (We have not yet received a sample for testing, but will verify these claims as soon as we do.)In the study partly led by Apple, more than 1,000 participants wore the Series 12 on one wrist, and another fitness tracker on the other. Apple compared the Watch to a Garmin Forerunner 970, Google Pixel Watch 4, Samsung Galaxy Watch 8, Whoop 5, Huawei Watch 5, and Oura Ring 5. Heart rate readings were taken by each device and a Polar H10 ECG chest strap, also worn by participants for accuracy purposes. Readings were taken during daily activities like running, cycling, strength training, desk work, meal prep, and resting, and then cross referenced with those from the chest strap. Based on the findings from this study, Apple claims the Series 12 shows the highest heart rate accuracy across devices.Shop the New Apple Watch Series 12 and Ultra 4Like many fitness wearables, the Apple Series 12 and Watch Ultra 4 use optical sensors (the green light on the back of a smartwatch, band, or ring) to measure heart rate and heart rate variability (HRV), which is the amount of time between beats. The new sensor system in both Apple watches includes larger green LEDs and enables higher-frequency heart rate measurements—every five seconds. These more frequent readings contribute to insights for your overall health on a daily basis. And as a runner, you can use these insights to train and recover better.How Heart Rate Helps You Become a Better RunnerSince your heart rate is usually a good indicator of how your body is responding to exercise, checking it mid-run can let you know if you’re on track with your workout. Likewise, if you notice your heart rate is too high on an easy run, you might slow your pace to stay in zone 2. Spending more time in this zone long term will help you build your aerobic base, and that’s one reason to invest in a device with a reliable sensor. But also, monitoring changes in your heart rate can help you better recover, and this is where HRV comes into play.AppleAppleTamanna Signh, MD, codirector of the Cleveland Clinic Sports Cardiology Center told Runner’s World in a previous interview that HRV symbolizes the balance between your fight or flight response, and your rest and digest system. A healthy HRV usually falls anywhere between 20 and 200 milliseconds, and a higher number is synonymous with having a very healthy nervous system, she said. “That means it’s able to drive high heart rates during workouts and then activate recovery mechanisms afterward.” It’s a personalized metric, so don’t compare your score to someone else’s; instead you should track how yours changes over time.Training load is another way Apple helps you balance running with recovery. The feature takes into account the intensity and duration of your workouts over the last 7 days in comparison to what you’ve done over the previous 28 days. It also takes into account heart rate. The goal is to help you avoid under- or overtraining—that’s it. With the Series 12 and Ultra 4, Apple will introduce training readiness and eventually roll out an app to the iPhone. It will give you more insights and actionable advice for training based on your heart rate readings and more, making accuracy even more essential.Is a Tracker With an Optical Heart Rate Sensor Right for You?It depends on how much you value accuracy, since heart rate is a temperamental metric to begin with. It’s easily influenced by external factors like weather, nerves, and sleep. For example, if you’re running in a hot and humid environment, your heart rate will spike. If you have trouble sleeping the night before a workout, perhaps because you’re nervous about hitting your paces, that can also influence your heart rate. You can’t rely solely on heart rate alone to train and recover. Many experts actually recommend considering it with other training variables like rate of perceived exertion on a run. Also, research shows external factors like skin tone can decrease the accuracy of optical sensors, so it’s harder to trust these readings alone.Luckily, optical sensors have been getting better and, if Apple truly has improved them this much, it makes the new versions of the Watch more reliable for runners. For now, this a step in the right direction. But, if you really need absolute accuracy, your best option is using what Apple used as its control: a chest strap.Explore The Best Heart Rate Monitors for RunnersMonique LeBrun is a health and fitness editor who is based in Easton, Pennsylvania. She covers a wide range of health and wellness topics, with a primary focus on running performance and nutrition. Monique is passionate about creating content that empowers runners to become the best versions of themselves. As an avid runner and parent, she loves spending time outdoors with her daughter, who often accompanies her on weekend runs as her personal mini run coach.