Fitness Tracker Accuracy Varies Across Devices, Studies Show

Validation research indicates that wrist‑worn fitness trackers are generally reliable for heart‑rate monitoring but perform poorly for calorie‑burn estimates. A 2017 Stanford University study of seven popular wearables, including the Apple Watch and Fitbit, found heart‑rate errors within 5 % but energy‑expenditure errors of about 31 % for walking/running and over 50 % for cycling. A 2025 meta‑analysis of 45 studies confirmed similar patterns, reporting roughly 76 % accuracy for heart rate, 69 % for step count and only 57 % for energy expenditure, with accuracy also affected by skin tone and age.

A personal field test comparing several devices during interval running on the Thames towpath found WHOOP and Fitbit AIR to track heart rate most closely, while the Garmin CIRQA consistently under‑reported heart rate. The Apple Watch Ultra 3 showed generally accurate readings but suffered occasional data dropouts. These findings highlight the variability of wearable sensor performance and the importance of device‑specific validation for users and researchers.