Smartwatch calorie estimates found to be inaccurate in new study

A study conducted by Florida International University, published in PLOS One, reveals that popular smartwatches often provide inaccurate estimates of calories burned during exercise. Researchers compared the readings of four devices—the Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5, and Garmin Forerunner 955—against clinical-grade laboratory equipment.

The findings indicate that typical errors in calorie estimation range between 15% and 25%. Among the tested devices, Apple was noted as the most accurate, while Garmin and Samsung showed the highest levels of overestimation. The study also noted that Fitbit experienced technical glitches during testing, producing implausibly low or missing readings.

Accuracy appears to decrease as body fat percentage increases, regardless of the device brand. Lead author Jason Kostrna warned that these discrepancies could lead users to believe they are in a calorie deficit when they are actually in a surplus, potentially undermining weight management efforts.