How Accurate Is a Fitbit and Other Smart Watches in Measuring Energy Expenditure?

Experts consider Fitbits surprisingly accurate , but they're not perfect. Because movement is subject to different factors, they're known to undercount or overcount steps at times. Walking on a plush carpet or pushing a shopping cart or stroller may cause Fitbit to undercount steps.

There is a common myth that people who eat in a calorie deficit but don’t lose weight are somehow defying the laws of thermodynamics. However, the more likely explanation is that the instruments used to track energy expenditure are not perfect. Most people rely on rough equations online, treadmill outputs, or smart watches to monitor their calorie burn.

A study conducted in 2018 showed that at that time, smart watches underestimated energy expenditure during exercise by 28 to 93%. This means that if a smartwatch displayed a calorie burn of 500, the actual calorie burn could be as low as 260. This discrepancy can lead people to believe that they are in a calorie deficit, when in reality, they are in a surplus.

A new study published in the European Journal of Sports Science examined the accuracy of three different smart watches: the Apple Watch 6, the Polar Vantage V, and the Fitbit Sense. They found that while all three watches did a decent job of measuring heart rate, they were all terrible at measuring energy expenditure. The coefficients of variation ranged from 15 to 25, indicating a significant margin of error.

If you are relying on a smart watch to monitor your calorie burn, it is essential to be aware of the potential inaccuracies. If you think you are eating in a calorie deficit and not losing weight, it is more likely that the instrument you are using to assess energy expenditure is inaccurate rather than you defying the laws of thermodynamics.

In conclusion, while smart watches can be helpful tools for tracking exercise and heart rate, they may not be accurate in measuring energy expenditure. It is essential to be mindful of the potential inaccuracies and not rely solely on a smart watch to monitor your calorie burn.


How accurate are calories burned on Fitbit?
The first sought to evaluate the accuracy of Fitbit to a measure calories burnt during aerobic exercise, and found they: Overestimated calories burnt by 26 – 61% during walking. Underestimated calories burnt by 37 – 59% during cycling. Overestimated calories burnt by 25 – 39% during jogging.
How accurate is the heart rate on a Fitbit?
The study compared generated electrocardiogram readings against readings from the PurePulse heart rate sensors in Fitbit's Charge HR and Surge trackers, and found that they can be off by up to 20 beats per minute during rigorous exercise.
What are the disadvantages of a Fitbit?
Obsession. There's awareness, motivation, competition. ... Tracking Errors. As with any device, it isn't perfect or fool proof. ... Connection. The device needs to connect with a smartphone and/or computer. ... Stands Out.
Do arm movements count as steps?
If you wear a fitness tracker on your wrist and you move your arms around (even if you aren't taking any steps) the sensor detects accelerations, which may be counted as steps. Hence steps for napkin folding (confessed by a waitress), drum playing, and more.