Apple Watch calorie counts far less accurate than heart rate or step tracking, review finds
Apple Watches and similar wearable devices exhibit significant inaccuracies when estimating calories burned, despite performing well in monitoring heart rate and counting steps.
A comprehensive review of 56 studies conducted by researchers at the University of Mississippi found that while fitness trackers are generally reliable for basic metrics, they struggle with energy expenditure calculations—a key feature many users rely on for weight management and fitness goals.
The analysis revealed that Apple Watches had a mean absolute percentage error of 4.43% for heart rate monitoring and 8.17% for step counts. However, the error rate for energy expenditure calculations rose sharply to 27.96%.
The inaccuracy in calorie tracking was consistent across all types of users and activities tested, including walking, running, cycling, and mixed-intensity workouts, suggesting the problem is not limited to specific use cases or user groups.
Professor Minsoo Kang, who specialises in sport analytics, and doctoral student Ju-Pil Choe conducted the meta-analysis to evaluate how device accuracy varied across different user demographics, health conditions, Apple Watch versions, and types of physical activity.
Data from the National Institutes of Health indicates that wearable technology has become increasingly popular across all demographics, from elite athletes to sedentary individuals. As early as 2015, approximately one in eight Americans reported using a wearable activity monitor. By 2019, wearable technology had become the leading fitness trend, with the market continuing to expand.
“If people are using them to make decisions about their workouts or even medical conditions, the data should be accurate,” Choe said. “If the numbers are off, it could lead to confusion, overtraining or even miss health warnings.”
The findings suggest that while Apple Watches can serve as useful support tools—such as for tracking basic activity levels during recovery from surgery—they should not replace clinical monitoring equipment or medical judgement.
These devices are great for keeping track of habits and staying motivated,” Kang said. “But do not take every number as 100% truth, especially the calories.
“Think of it as a helpful guide, not a diagnostic tool. It is useful but not perfect.”
The researchers noted that newer Apple Watch models appeared to demonstrate improved accuracy compared to earlier versions, suggesting ongoing technological refinements.
“While we cannot say every update is a big leap forward, there is a noticeable trend of gradual improvements over time,” Choe said. “It shows that Apple is refining the technology over time.”
The study’s implications extend beyond consumer awareness to potential improvements in wearable technology development. Kang explained that identifying specific weaknesses could help manufacturers enhance their products.
“By showing where the weaknesses are, we can help developers get real feedback,” he said. “If they know what needs to be fixed, they can design better sensors or algorithms.
Our findings can guide improvements and help make these devices more useful for both everyday users and health care providers.”
The research highlights the importance of understanding the limitations of consumer health technology, particularly as these devices become increasingly integrated into both personal fitness routines and healthcare monitoring systems.
For older adults and those managing chronic conditions who may rely heavily on wearable devices for health tracking, the findings underscore the need to view such technology as supplementary rather than definitive health monitoring tools.
