Your smartwatch may be overestimating calories burned by 25 percent

September 2, 2026

New research shows popular smartwatches can overestimate calories burned during exercise by 15–25 percent, with Apple Watch the most accurate and Garmin and Samsung the least. In controlled tests against clinical-grade metabolic analyzers, some devices were so unreliable (Fitbit Sense 2) that data had to be discarded due to glitches.

The miscalculations matter for weight management: a claimed 500-calorie workout might really be closer to 350, potentially turning an intended calorie deficit into a surplus over time. Accuracy also tended to worsen for wearers with higher body-fat percentages, likely because companies’ proprietary algorithms are built on opaque training data. Researchers recommend treating smartwatch calorie numbers as optimistic estimates and focusing on overall trends and how you feel rather than precise figures. PopSci