How Much Should You Trust Your Smartwatch Health Data?

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There’s something about seeing a number on your wrist that makes it feel like a fact. Your watch tells you your heart rate hit 190 beats per minute, you spent an hour and 40 minutes in deep sleep, or you burned exactly 684 calories, and you’re inclined to believe it.

But how accurate are those numbers, really?

That question matters more as smartwatches take on a bigger role in tracking our health. Apple, for example, rolled out the Watch Series 12 this month with more frequent heart-rate sensing and a new readiness score, while Google has promised improved sleep-stage detection on the Pixel Watch 5.

The problem, though, is that health data can look more precise than the technology measuring it actually is. Research suggests the useful question isn't whether a smartwatch is accurate or inaccurate, but how much confidence we should place in a particular reading.

Shalom*, an Apple Watch Series 9 user, found that out during a workout when his watch suddenly showed a heart rate of around 190 beats per minute.

“There is no way I'm at 190,” he remembers thinking.

He slowed down and watched the number fall. Without another monitor, he couldn't tell whether the watch was wrong. But the experience changed how he viewed the data.

“I still use it,” he said, “but I don't treat every number as fact anymore.”

How accurate is smartwatch heart-rate data?

Heart rate is one of the better-supported measurements on consumer wearables, although performance varies by device and activity.

A 2026 study compared 10 commercial wearables with heart-rate measurements derived from an electrocardiogram, or ECG, in 45 adults. The Fitbit Charge 6 recorded a median mean absolute error of 4.5 beats per minute, while the Google Pixel Watch 2 recorded 4.9.

Four other devices: the Polar Ignite 3, Polar Pacer, Oura Ring Gen 3, and Fitbit Inspire 3, recorded median errors ranging from 9.5 to 14.3 beats per minute.

When movement was considered, intermittent walking increased errors across several devices.

For someone wearing the watch, that means a steady resting reading may deserve more confidence than a sudden number recorded while movement is changing.

Shalom has seen the more reassuring side, too. On one occasion, he manually counted a resting heart rate of around 70 beats per minute while his Apple Watch showed 69 or 70.

For him, repeated patterns now matter more than individual readings.

“If it was something like an unusually high heart rate that kept happening while I was resting, I'd probably take it seriously and check it with another device or speak to a doctor,” he said.