Smartwatch Calorie Trackers Have Proven Inaccurate

A new study found popular wearable devices consistently overstated calorie burn during controlled exercise sessions.

Updated on Sept. 21, 2026 in Nutrition

Bold vector editorial illustration showing a sleek, matte fitness wrist-band, illustrating the inaccuracy of wearable health monitoring devices. — A Florida International University study found popular consumer smartwatches consistently overestimated calorie burn by 15% to 25% during exercise. AI Illustration. Upload story photo >

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Do you trust your fitness tracker to provide accurate calorie burn information for your health goals?

Researchers at Florida International University tested four major smartwatches against clinical metabolic equipment, finding that all devices provided inaccurate estimates. Every model overstated calories burned, with error rates typically ranging between 15% and 25%.

Why it matters

The study highlights a significant gap between consumer wearable technology and clinical-grade health monitoring. These findings suggest that relying solely on device data for precise nutrition or fitness management may lead to flawed health calculations.

A study of 58 adults during bike workouts measured performance across four popular smartwatch models. Researchers found error rates between 15% and 25%, with the Apple Watch Series 8 proving most accurate while Garmin and Samsung showed higher overestimations.

The players

Florida International University

This is a public research university located in Florida that conducted the comparative study on wearable health technology.

Apple Watch Series 8

This is a consumer smartwatch model manufactured by Apple that demonstrated the highest relative accuracy in the study.

Fitbit Sense 2

This is a wearable device model by Fitbit that occasionally failed to produce calorie readings during the clinical trials.

Samsung Galaxy Watch 5

This is a smartwatch produced by Samsung that was among the devices showing high calorie overestimation in the study.

Garmin Forerunner 955

This is a high-end sports watch model from Garmin that, along with Samsung devices, produced the highest calorie overestimations.

The details

The Florida International University research team evaluated the Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5, and Garmin Forerunner 955 using a COSMED K5 metabolic analyzer as a benchmark. Participants performed a routine on a recumbent bike that alternated between moderate and vigorous intensities, during which Fitbit devices occasionally failed to record data.

The study findings were published on September 21, 2026.

The Big Picture

This research follows a pattern set by the use of the COSMED K5 metabolic analyzer in medical-grade studies to validate human energy expenditure. By testing consumer technology against this standard, the study provides a necessary reality check on the clinical utility of wearables.

Users should be aware that their smartwatch calorie burn estimates may be significantly inflated by 15% to 25% during moderate to vigorous activity. Relying on these numbers for strict diet or weight loss planning may require adjusting caloric intake targets to compensate for device inaccuracies.

The takeaway

Consumers should treat wearable calorie estimates as general movement indicators rather than precise biological measurements. Maintaining a balanced approach to exercise and nutrition remains more reliable than trusting automated device data for specific health outcomes.