The Apple Watch is pretty accurate — at least for certain metrics.
A new University of Mississippi meta-analysis of 56 studies finds the Apple Watch delivers fairly accurate data for heart rate and step counts — but shows a much wider margin of error when it comes to calories burned.
In the year 2025, wearable tech is almost startlingly common. If you walk into any gym in the United States, chances are you’re going to see wrists adorned with some kind of fitness tracker or smartwatch.
And it makes sense, too. Whether you’re concerned about your health or just looking to dial in your workouts, wearing an Apple Watch — or any other fitness tracker — seems like an ideal way to do it.
But that begs the question — just how accurate are health trackers like the Apple Watch? That’s the exact question that University of Mississippi researchers set out to answer.
The Apple Watch knows how much you move, not how much you burn
The Ole Miss study analyzed data from 56 studies comparing the Apple Watch data to clinical reference tools. Researchers took factors like age, existing health conditions, device age, and activity into account.
And, as it turns out, the Apple Watch is, well, fairly accurate.
If you’re using yours to track your heart rate or step count, they’re quite accurate. The study found mean absolute percent errors, a standard measure of accuracy, of 4.43% for heart rate and 8.17% for step counts.
Energy, expenditure, on the other hand, was notably less accurate. The study showed that when it came to tracking calories burned, the Apple Watch was inaccurate nearly 28% of the time.
The energy expenditure inaccuracy was observed across all types of users and activities tested, including walking, running, cycling, and mixed-intensity workouts.
The Apple Watch remains a useful tool, not a diagnostic device
So you may be wondering if this means you should throw your Apple Watch into the trash. Obviously, it doesn’t.
University of Mississippi professor Minsoo Kang, who headed the study, still thinks these trackers have a place.
“These devices are great for keeping track of habits and staying motivated, but do not take every number as 100% truth, especially the calories,” he told Eureka Alert. “Think of it as a helpful guide, not a diagnostic tool. It is useful but not perfect.”
While they’re not perfect now, that doesn’t mean they’re not improving over time, either. Newer models of Apple Watch appear to be significantly more accurate than previous iterations.
“While we cannot say every update is a big leap forward, there is a noticeable trend of gradual improvements over time,” Doctoral student Ju-Pil Choe said. “It shows that Apple is refining the technology over time.”
Kang remains optimistic about the future of wearable tech. He hopes that the study can help users make informed decisions about purchasing wearable tech and that it could help inspire fitness tech creators to reexamine where devices fall short.
“By showing where the weaknesses are, we can help developers get real feedback,” he says “They know what needs to be fixed, they can design better sensors or algorithms.”
“Our findings can guide improvements and help make these devices more useful for both everyday users and health care providers.”
