Smartwatch calorie tracking shows significant inaccuracies

Researchers from Florida International University have found significant inaccuracies in how popular smartwatches estimate calorie expenditure. A study involving 58 adults compared data from four major devices—Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5, and Garmin Forerunner 955—against a metabolic analyzer, which is considered the gold standard for measuring energy expenditure.

The findings revealed that calorie estimates from these devices deviated from actual consumption by an average of 15 to 25 percent. Because smartwatches use algorithms to predict energy output based on heart rate, movement, age, and weight rather than measuring it directly, factors such as body composition, fitness levels, and physiological responses can lead to substantial errors. The study noted that error rates tended to increase in participants with higher body fat percentages.