This entirely depends upon the individual tracker and how this accuracy is gauged against other similar devices from different brands. Some brands of trackers may show readings that are one or two calories off, whereas another device may display readings that are far off from the readings that you are getting on another device. With this in mind, Garmin, Apple, and Fitbit have consistently received standout reviews over the years in terms of their activity tracker accuracy when it comes to calories and other fitness metrics.