How Does Fitbit Track Calories Burned?

How does my Fitbit device calculate calories burned? Fitbit devices combine your basal metabolic rate (BMR)—the rate at which you burn calories at rest to maintain vital body functions (including breathing, blood circulation, and heartbeat)—and your activity data to estimate your calories burned.

Are you struggling to lose weight even though you are eating in a calorie deficit? You might want to reconsider the accuracy of the instrument you are using to track your energy expenditure. In this blog post, we discuss the accuracy of smartwatches, such as the Fitbit, in measuring the number of calories burned.

Most people track their energy expenditure using rough equations from the internet, treadmill output, bike output, or smartwatches. However, a study conducted in 2018 showed that smartwatches underestimated energy expenditure by 28% to 93% during exercise. This means that if a smartwatch indicates that you burned 500 calories, you might have burned only 260 calories.

A recent study published in the European Journal of Sports Science compared the accuracy of three new smartwatches- Apple Watch 6, Polar Vantage V, and Fitbit Sense. They found that the Apple Watch 6 was the best at measuring heart rate, but all three watches did a poor job of measuring energy expenditure, with coefficients of variation ranging from 15% to 25%.

Therefore, 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 measure energy expenditure is inaccurate rather than you defying the laws of thermodynamics.

In conclusion, it is important to be aware of the limitations of the instrument you are using to track energy expenditure. While smartwatches have improved over the years, they are still not accurate enough to be relied upon solely for measuring calories burned. It is best to combine smartwatch data with other methods of tracking energy expenditure, such as heart rate monitors or simply focusing on your diet and exercise routine.

If you are interested in staying up-to-date with the latest research on training and nutrition, check out our new research review, Reps. We break down five studies related to training and nutrition every month and explain how they affect you. Click the links in the description to learn more.


Is Fitbits calories burned accurate?
If your Fitbit says you're burning more calories than you actually are, don't worry. Remember that the calorie burn estimate is just that—an estimate. It's not going to be 100 percent accurate.
How does Fitbit track how many calories you burn?
Fitbit devices integrate measurements of basal metabolic rate and breathing, heart rate, and other daily physical activity data to accurately measure the number of calories burned. Basal metabolic rate is calculated by manually logging data into the app such as sex, age, height, and weight.
How does Fitbit track calories burned when not wearing?
These are the calories you burn just keeping your body alive (even when asleep). They are calculated from your profile settings for age, height, weight etc so you needn't be wearing your fitbit to get them. What you are seeing in the morning is the total BMR calories burned since midnight.
Why does my Fitbit say I burned so many calories?
It's based largely on your basal metabolic rate (BMR) or the energy your body expends at rest—even when you're sleeping! —just to keep you alive. BMR powers basic but vital life processes, like breathing and thinking, and accounts for most of your daily calorie burn.