Your Fitness Tracker Probably Isn’t Accurately Calculating the Calories You Burn

Your fitness tracker might not be accurate. Photo: Getty Images

New research adds to the mounting evidence that your fitness tracker might not actually help you lose weight: Although these devices can help monitor your heart rate, they’re unreliable when it comes to calculating the amount of calories you actually burn, according to a study.

Researchers from Stanford University evaluated seven different fitness devices — Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, and the Samsung Gear S2 — used by 31 women and 29 men, the Guardian reports. The participants wore their devices while walking or running on the treadmill, cycling on exercise bikes, or sitting still — and none of the devices measured energy expenditure (or calories burned) properly.

Of the group, the most accurate device at calculating energy expenditure was the Fitbit Surge, even though its calculation was still off by an average of 27.4 percent, according to the Guardian. The highest margin of error, however, was on the PulseOn device, which had an average error of 92.6 percent. However, calories-burned data from the Samsung device was not available.

“When you consider that people are using these estimates to essentially make lifestyle decisions like what they are going to eat for lunch then I think that is something that is worth knowing and people should know to take these estimates with more than a pinch of salt,” study co-author Dr. Euan Ashley told the Guardian.

In contrast, the devices were found to be quite accurate at measuring heart rate, according to the study, which was published in the Journal of Personalized Medicine. The most accurate heart rate readings were from the Apple Watch — which had an error rate of about 2 percent — and the least accurate came from the Samsung Gear S2 device, which had a median error in heart rate of 6.8 percent.

Despite the inaccurate calories-burned calculations, the researchers said fitness trackers may still be valuable, given the successful heart rate monitoring. “More attention to diet and exercise is always going to improve the health of our population,” Ashley said.

Your Fitness Tracker Isn’t Accurately Counting Calories