Researchers from Florida International University have shown that smartwatches from leading brands overestimate calorie burn by up to 25%, with the margin of error increasing alongside the user's level of obesity.

The study evaluated the Apple Watch Series 8, Garmin Forerunner 955, Samsung Galaxy Watch 5, and Fitbit Sense 2, comparing their readings against medical-grade equipment. Garmin showed an average discrepancy of 69 kcal, Samsung 57 kcal, and Apple 22 kcal. Fitbit had an average deviation of 3 kcal but also exhibited extreme fluctuations and data loss.

The algorithms were calibrated primarily using lean individuals, which explains the greater discrepancies observed in overweight users.

Conclusion: Commercial smartwatches remain insufficiently accurate for precise individual calorie budgeting or rigorous clinical/research monitoring; users should treat caloric metrics as relative general trends rather than absolute values.