Smartwatches often miscalculate calorie burn, FIU study finds

Researchers at FIU evaluated the Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5, and Garmin Forerunner 955 against clinical-grade metabolic analyzers. During trials involving 58 adults on recumbent bikes, the team found typical estimation errors ranging between 15% and 25%. While the Apple Watch proved the most accurate of the group, Garmin and Samsung devices recorded the highest overestimations. The Fitbit data proved difficult to verify, as the device suffered repeated glitches that forced researchers to discard portions of the data.

Jason Kostrna, the study's lead author and an associate professor of kinesiology, warns that relying on these inflated numbers can derail weight management efforts. Because users might inadvertently enter a calorie surplus while believing they are in a deficit, Kostrna suggests treating device readouts as a conservative ceiling rather than a precise metric. He advises focusing on secondary data like heart rate zones and long-term personal trends rather than fixation on a single day’s calorie total. The research team is now shifting its focus to evaluate how these wearables perform during traditional strength-training sessions.