Consumer fitness wearables overestimate calories burned by 15‑25%, especially for users with higher body fat, with Apple Watch performing best among tested brands.
A study led by associate professor Jason Kostrna of Florida International University found that consumer‑grade fitness wearables typically overestimate calories burned by about 15% to 25%. The magnitude of the error increased with the wearer’s body‑fat percentage; individuals with 35%‑40% body fat saw reported calories roughly double the actual amount burned.
Kostrna explained that wrist‑worn devices combine user‑entered data (age, gender, height, weight) with heart‑rate and accelerometer signals to calculate energy expenditure, and the algorithms appear less calibrated for higher‑fat individuals.
Heart‑rate measurements were generally accurate, within a beat or two, while calorie estimates varied by brand. In the tests, the Apple Watch showed the smallest error, whereas Samsung, Garmin and Fitbit devices exhibited larger discrepancies.
The researchers advise users to treat calorie estimates conservatively, particularly if they have higher body fat. The study’s error rates differ by individual characteristics and device model, and the findings are limited to the devices and participants examined.