How does Fitbit calculate calories?

In this guide, we will discuss “How does Fitbit calculate calories” and some additional things to consider when using Fitbit to track your calories burned during the day (and night).

How does Fitbit calculate calories?

We will talk about how Fitbit calculates calories. Fitbit devices combine your BRM or basal metabolic rate, the rate at which you burn calories at rest allowing you to maintain vital functions (breathing, blood circulation and heartbeat) and your activity data to estimate calories burned. If your device has a heart rate sensor, your heart rate data will also be included, especially to estimate calories burned during exercise. 

Moreover, the number you will see on the display corresponds to the total of calories burned a day. However, remember that the BRM is based on your personal information such as height, weight, sex and age, and it will account for half of the calories you have burned in a day. Consider that your calories will still be calculated even if you are sleeping, you may notice the number will be displayed when you wake up and it will increase during the day.

Finally, for certain regions, you will see kilojoules instead of calories but you can change the units of measurements by going to the settings on the device. If you are using the Fitbit app, tap the Today tab and then your profile picture. Next, tap advanced settings and then Units. Make the changes. For the Aria 2, you have the option to change the units shown on the scale following the instructions:

  • Tap the Today tab and then your profile picture. Next, tap on your scale icon.
  • Tap Weight Units and choose the units you prefer the scale to show your weight in. The next time you sync your scale, you will see your weight in the units selected. 

Basal metabolic rate (BMR)

Your BMR is an estimate of how much energy your body uses while at rest or when you are not performing any demanding physical activity such as running or dancing. Your Fitbit calculates or roughly estimates your BRM by using the personal data you have provided initially. 

Moreover, this is the reason why your Fitbit will still burn calories even when you haven’t been exercising and just lounging around watching TV all day. However, remember that your body is burning calories all the time, even if you are sleeping. Other data considered to determine an individual’s BMR are their breathing rate, blood pressure and heart rate.

Heart Rate 

You may have heard by now that Fitbit can measure your heart rate even if it can measure your breathing rate and blood pressure. The heart rate measure will help estimate and improve calorie burn. Generally speaking, a higher heart rate means a faster metabolism while a slower rate implies that you are burning them at a slower rate. 

Some examples are the Fitbit Ionic, Fitbit Blaze, Fitbit Versa, Fitbit Versa 2, Fitbit Charge 2 and Fitbit Charge 3. 

Daily Steps

Every Fitbit tracker has this feature included, where you can monitor how many steps you have taken each day. Not only this device will help detect and measure when you are active but also will let you know how much you do or don’t move. 

Fitbit uses this kind of information and other data, as we have discussed, to help estimate the calories burned. 

Why does my calorie allowance change during the day?

According to Danielle Kosecki from, “There are a couple of reasons. But first, it may be helpful to know a little bit more about calorie allowances and how yours is calculated”.

For this, we need to understand what a calorie target is. Simply put, it is the calorie target you set as a daily goal or the max amount of calories you should be eating a day. Having this type of goal is important so it can give you a target to aim for and this way it will help you to avoid over or under eating.

It is not a secret that a balanced diet is key when you are trying to lose weight and not only for this purpose but also to keep good health. Experts believe that weight depends on how many calories you consume a day vs the number of calories you are burning. This could happen through exercise, daily low impact physical activity or due to your body’s baseline metabolism.

For instance, having a hypocaloric diet means you will be reducing your daily calorie intake or having foods with high caloric density to help you lose weight. However, always consult with a physician or nutritionist if you are planning to make drastic changes to your diet.   

How does Fitbit calculate my calorie target?

If you use the Fitbit app or if you go to dashboard, you can create a food plan after you have entered your current weight and your goal weight. If you are wanting to lose or maintain weight, you can set the planned intensity to Easy, Medium, Kinda Hard or Harder. This can help Fitbit determine how high to set your calorie deficit, meaning how many fewer calories you need to eat to maintain or lose weight. 

The calculations are based on the basic knowledge that 3,500 calories equal about one pound of fat. Subsequently, to lose one pound you will need to eat 3,500 calories on average each week or burn 3,500 calories more than the ones you are consuming. 

Additionally, you can also set your calorie target manually. For instance. If you would like to lose 50 pounds, you can choose a medium or kinda hard intensity plan where the Fitbit will indicate a daily calorie deficit of 500 to 750 calories, which will allow you to lose one pound a week. 

Daily Calorie ‘Estimate’

After you have chosen an intensity you are practically set but don’t expect the Fitbit dashboard to always show a fixed calorie target even if it seems efficient, it will certainly not help much in your weightloss journey. This is because the key numbers here are your calorie deficit and not your target, which can fluctuate depending on the activity level. 

As advised in, “instead of only doing the simple math for you (ie: Your calorie target is 2,000. You’ve eaten 1,500 calories. Therefore you have 500 calories left to eat), Fitbit pulls in other data to calculate your Daily Calorie Estimate, a much more personalized and dynamic metric that uses your average activity to predict how many calories you should eat each day”.

Why is this blog about How does Fitbit calculate calories important?

As we have discussed how Fitbit calculates calories, we have seen that there is no magic formula. It is an estimate resulting from various measurements and data provided by you (i.e. height, weight, age) and the measurements collected by the Fitbit (i.e. Heart rate, daily steps, the intensity of the physical activity). Moreover, determining how many calories you have burned throughout the day will allow you to set yourself a weight loss goal or it may help you also if you are trying to maintain it. 

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Frequently Asked Questions (FAQs) about How does Fitbit calculate calories

Is Fitbit accurate for calories?

Fitbit has been suggested to be accurate when counting calories burned. A study found that the Fitbit Surge had the most accurate calories burned calculation among a group of similar devices with just an error rate of over 25%. Other similar devices tested had comparatively higher error rated up to 93%. 

How does Fitbit calculate calories burned?

Fitbit calculates calories burned using both specific information about you and more general calculations pre-loaded into the algorithm, including calculations about how other people burn calories writ large. 

Does Fitbit overestimate calories burned?

“Fitbits and other trackers are overestimating the number of calories burnt during walking, scientists have said”, according to Researchers have found that one of the best selling options (Fitbit Charge 2), was fairly accurate when estimating the number of calories burned while running, underestimating by only four percent.  

Why does my Fitbit tell me I’ve burned so many calories?

Your Fitbit tracker’s calories-burned tally resets each night at midnight. So the number you see on your tracker (or in your Fitbit app) first thing in the morning is your estimated calorie burn for the day so far.

How can I burn 500 calories a day?

If you would like to burn 500 calories a day, here are some physical activities or exercises that will even help you burn them in an hour:

Weight lifting.

References How does my Fitbit device calculate my daily activity? Ask Fitbit: Why Does My Calorie Allowance Change Throughout the Day?