Wearable Fitness Trackers: How Accurate Are They Really?

What trackers tend to measure reasonably well

Step counting and heart rate during steady-state activity are generally reasonably accurate across most modern consumer devices, having improved considerably in reliability over the past several years of sensor development.

Where accuracy genuinely drops off

Calorie burn estimates remain notably imprecise across nearly all consumer devices, often off by a meaningful margin, since they're calculated from indirect proxies (heart rate, movement) rather than direct measurement.

Sleep tracking's genuine but limited usefulness

Most wearables can reasonably distinguish sleep from wakefulness, but detailed sleep-stage breakdowns (deep, REM, light) are considerably less accurate compared to clinical sleep study equipment — useful for general trends, less reliable for precise detail.

How to use tracker data most usefully despite these limitations

Focusing on personal trends over time, rather than treating any single day's exact numbers as precise fact, extracts most of the genuine value from these devices despite their inherent measurement limitations.