Smartwatches may provide inaccurate calorie‑burn estimates

Smartwatches and fitness trackers have become ubiquitous tools for monitoring exercise, but recent studies suggest they may significantly overestimate the number of calories burned during workouts. Researchers from the University of Washington tested 50 participants across a range of activities—including running, cycling, and high‑intensity interval training—using both consumer-grade smartwatches and a gold‑standard metabolic cart. The devices consistently reported calorie counts that were 15 % to 30 % higher than the measured values, with larger discrepancies observed during high‑intensity sessions.

The discrepancy stems from the algorithms that smartwatches use, which rely on heart‑rate data, movement sensors, and user‑entered inputs such as age, weight, and gender. These inputs are often generic or self‑reported, and the devices assume a fixed relationship between heart rate and energy expenditure that does not account for individual metabolic differences, fitness level, or the specific biomechanics of each exercise. Manufacturers have acknowledged the limitations but argue that the estimates are still useful for tracking relative changes over time rather than precise calorie counts.

While the inaccuracies mean that users should be cautious about using smartwatch data for calorie‑controlled diets or precise training metrics, the technology remains valuable for general activity monitoring and motivation. Experts recommend pairing device data with periodic laboratory testing or using it in conjunction with other health metrics to get a more complete picture of fitness progress.