How does Fitbit calculate calories burned?

In this brief guide, we are going to answer the question “How does Fitbit calculate calories burned” and provide you with more tips on how to track your calories using your Fitbit tracker.

How does Fitbit calculate calories burned?

The Fitbit uses the information you give when first creating a profile, such as your age, weight, height and gender to establish a Basal Metabolic Rate (BMR). The BMR determines the calories you burn while at rest. 

Calories burnt at BMR are due to inner body functions such as breathing, digestion and blood circulation etc. Fitbit also uses your resting heart rate and heart rate variability to calculate your BMR and make an estimate of calories burned.

What are calories

According to an 1863 article in the Journal of Nutrition, titled “History of the Calorie in Nutrition,” a Calorie was defined as “the amount of heat needed to raise the temperature of 1 kilogram of water from 0 to 1 degree Celsius”. In 1925, calories were scientifically defined in terms of joules in which 1 joule is the amount of energy needed to force 1 Newton through 1 metre. 

 In terms of calories, one calorie is the equivalent of 4.18 joules. The term Calorie is often used to represent kilocalorie and is shortened to kcal which is widely seen at the back of food products to represent their nutritional values.

What parameters does Fitbit use to calculate calories burned?

This basal rate accounts for half the calories burnt throughout the day. The rest of the calorie count comes from step count, exercise or elevated heart rate during work. 

Heart Rate

Fitbit devices continuously log your heart rate. The algorithms at work make use of heart rate data to calculate an estimate of calories burned. Generally, a higher heart rate translates to a faster metabolism and a slower heart rate implies that your calories are being burned slowly.


Step count

All Fitbit trackers track your daily step count, this is suggestive of your activity level and this information can be used to calculate the number of calories you burn


Tracked Exercises

Fitbit allows you to log different exercises in the Fitbit app, with your height and weight stats Fitbit calculates the number of calories you burn during these exercises and this number is added to your daily total

How accurate is the calorie count?

All this information is based on sensors that measure, for example, the step count but any other activity that mistakenly registers as step count would also cause an increase in calorie count.  

Stress can also contribute to an elevated heart rate and this can also be misjudged as an activity that raises heart rate and may give a distorted calorie count.

This makes the calorie count readings a lot less accurate than individual heart rate readings, step count and oxygen saturation levels because of the added parameters.

Algorithms at work take in many factors to calculate the calorie burned but as more parameters are added, the accuracy is bound to decrease.

How is the calorie count useful?

It can easily be debated that even if the tracker is inaccurate, it still logs daily progress. The inaccuracy would be by the same number of points, each day. 

Hence, if you sit around most days, the app will clearly show a change in calories when you decide to go for a walk.

Accuracy aside, an approximate number of calories burned would still benefit the Fitbit user, who is willing to add an exercise regime to their daily routine. 

A higher number of calories burned would still be a good motivator for someone willing

to lose weight.

How to increase my calories burned?

It is useful to know that cardiovascular exercises are a great way to burn calories. When you wear your Fitbit during exercise, it measures your heart rate. It places your heart rate activity in three different zones


Intensity: Vigorous (85 to 100 percent of your max heart rate)


Intensity: Hard (70 to 84 percent of your max heart rate)

Fat Burn

Intensity: Moderate (50 to 69 percent of your max heart rate)

Burn fat fast during exercising

During the fat burn zone, your body is using fat as fuel. If you are willing to lose weight, it would be advisable to stay for longer periods within this range to maximize your weight loss and burn that extra fat.

You can track your heart rate while exercising, and target to stay in the heart rate zone that you desire.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         How to use the Fitbit Calorie Counter

The Fitbit app for iOS, Android and Windows now comes with a calorie-counting feature as well. This lets you manually log your food and it records an estimate of the calories consumed from that food. This feature allows you to compare your daily calorie consumption, and compare it to the calories you burn throughout the day.

To manually add food:

1. Tap the Today tab, tap the icon on the food tile.

2. Search for your food or create a custom food.

3. Enter your information and tap Save.


In this brief guide, we answered the question “How does Fitbit calculate calories burned?”, and provided you with more tips on how to track your calories with the Fitbit fitness tracker.

If you have any questions or comments please let us know.