Fitness tracker users can rely on their gadgets for heart rate information, but not so much on the number of calories burned. According to a new study, data on calorie expenditure on major fitness tracker brands is extremely unreliable, with up to 27% deviation in the most accurate reading, and up 93% deviation in the least reliable devices. Researchers aren’t sure what exactly accounts for such inaccuracies: each device uses its own proprietary algorithm to calculate energy expenditure, so it’s hard to tell how the number of calories burned is calculated. Study authors have made their data available to the public, and invite fitness tracker users to share their accuracy performance data.


Anna Shcherbina, C. Mikael Mattsson, Daryl Waggott, Heidi Salisbury, Jeffrey W. Christle, Trevor Hastie, Matthew T. Wheeler and Euan A. Ashley

Corresponding author:

Euan A. Ashley, Cardiovascular Medicine, Stanford University, CA, US, Email:

Open data from the study:

Original paper published in the Journal of Personalized Medicine on May 24, 2017.