Your Smartwatch Could Be Overestimating How Many Calories You Burn

Smartwatches have become popular tools for tracking exercise, heart rate, steps, sleep and calorie expenditure. For people trying to lose weight or maintain their fitness, the calorie-burn figure displayed after a workout can seem especially useful.

However, new research suggests that number may not be as precise as many users assume.

A recent study involving 58 adults found that several popular smartwatches produced significant errors when estimating calories burned during cycling exercise. While some devices performed better than others, researchers found that none of the four tested brands consistently provided an exact measurement of energy expenditure.

The findings suggest that smartwatch calorie estimates should be viewed as general guidance rather than precise measurements.

Smartwatch Calorie Estimates Can Be Off by 15% to 25%

Researchers asked 58 adults to complete a cycling workout while wearing four widely used smartwatch brands. The calorie estimates recorded by the devices were then compared with measurements from clinical-grade equipment designed to assess actual energy expenditure.

The results showed considerable differences between the smartwatch readings and the clinical measurements.

In general, the devices were inaccurate by roughly 15% to 25%. Although the Apple Watch produced the closest estimates among the devices tested, it still overestimated calorie expenditure by approximately 22 calories on average.

Samsung's device overestimated calorie burn by around 57 calories, while Garmin's estimate was nearly 69 calories higher than the measured energy expenditure.

Fitbit presented an additional challenge. Researchers found that approximately 13% of Fitbit trials generated unusually high readings. Those results were excluded from the primary analysis because they were considered implausible.

These findings do not necessarily mean that every calorie estimate from a smartwatch is wrong by the same amount. Instead, they demonstrate that the margin of error can be large enough to matter, particularly for people who use wearable data to guide their eating and exercise habits.

Why Calorie Accuracy Matters for Weight Management

For someone simply interested in monitoring activity, a calorie estimate that is somewhat inaccurate may not make much difference.

The situation can be different for people using smartwatch data to calculate a daily calorie deficit.

For example, imagine a person completes a workout and their smartwatch reports that they burned 500 calories. They may then believe they have created a significant calorie deficit and feel comfortable eating more food later in the day.

If the actual energy expenditure was substantially lower, the person's calorie deficit could be much smaller than expected. Repeating this pattern several times a week could eventually affect weight-management results.

This is why researchers caution against treating wearable calorie estimates as exact measurements.

Small daily differences can accumulate over time. Someone who regularly overestimates exercise-related calorie expenditure could unintentionally consume more calories than they burn while believing they are following a calorie-deficit plan.

Body Fat May Also Affect Accuracy

The research identified another important factor that could influence smartwatch performance.

According to the study, calorie-estimation accuracy declined as body fat increased. This pattern was observed across all four smartwatch brands included in the research.

Wearable devices generally use information such as heart rate, movement, body characteristics and other measurements to estimate energy expenditure. These calculations are based on algorithms rather than a direct measurement of every calorie a person burns.

Because human bodies differ significantly, an algorithm that works relatively well for one person may produce less accurate results for another.

Factors such as body composition, fitness level, exercise intensity and individual physiology can all influence energy expenditure.

This means that smartwatch calorie numbers should not automatically be considered personalized laboratory measurements.

Your Watch Is Still Useful for Tracking Exercise

The research does not mean that smartwatches are useless.

Wearable technology can provide valuable information about exercise habits and can make it easier to monitor activity over time. Heart rate readings, workout duration, step counts and heart-rate zones can help users understand how their activity changes from one day to the next.

The key is knowing how to interpret the information.

Instead of focusing heavily on a single calorie number, users may benefit from looking at longer-term trends. For example, tracking how frequently you exercise, how long you remain active and how your heart rate responds to workouts can provide useful information without requiring the calorie estimate to be perfectly accurate.

A smartwatch can therefore function as a helpful fitness-tracking tool without being treated as a calorie-counting authority.

Consider Using Calorie Numbers as Estimates

Researchers recommend taking smartwatch calorie-burn figures with caution.

One practical approach is to assume that the displayed number may be higher than your actual expenditure. Rather than automatically eating back every calorie reported by your device, you could use the figure as a rough estimate and consider a more conservative interpretation.

For people managing their weight, other measurements may also provide useful context.

Changes in body weight over several weeks, waist measurements, workout performance and overall eating patterns can provide a clearer picture than relying on a single daily calorie estimate.

It is also important to remember that calorie expenditure naturally varies from person to person. Two people completing the same workout may not burn exactly the same amount of energy.

More Research Is Needed

The researchers behind the study plan to investigate whether smartwatches perform differently when measuring calorie expenditure during strength-training workouts.

That research could be particularly useful because resistance training presents different challenges for wearable devices compared with steady-state activities such as cycling.

Smartwatch technology continues to develop, and manufacturers regularly update their sensors and algorithms. As wearable devices become more sophisticated, their ability to estimate physiological measurements may improve.

Still, consumers should remain aware of the limitations of wearable technology.

A smartwatch is designed to provide convenient estimates based on available sensor data. It is not the same as having energy expenditure measured in a controlled clinical or laboratory setting.

The Bottom Line

Smartwatches can be valuable companions for people who want to become more active, monitor workouts or understand their fitness habits. However, new research suggests that the calorie-burn numbers displayed by these devices can be significantly inaccurate.

In a study of 58 adults performing cycling workouts, all four tested smartwatch brands showed substantial errors. Some devices overestimated calorie expenditure by dozens of calories, while one brand produced unusually high readings in a portion of its trials.

For anyone using a smartwatch for weight management, the safest approach is to treat calorie-burn figures as estimates rather than exact numbers.

Instead of asking whether your watch says you burned 300, 500 or 700 calories, pay attention to broader trends in your activity, heart rate, workouts and eating habits.

Your smartwatch can still be a useful fitness tool. Just remember that when it comes to calories, the number on your wrist may not tell the whole story.

Source

Florida International University.

Medical Disclaimer

This article is intended for general informational and educational purposes only. The information provided should not be considered a substitute for professional medical advice, diagnosis or treatment. Statistical findings from medical research describe trends within study populations and may not apply directly to every individual. Calorie needs and energy expenditure can vary substantially based on factors such as age, body composition, activity level, health status and individual physiology. If you have questions about weight management, nutrition, exercise or your personal health, consult a qualified healthcare professional for advice tailored to your circumstances.