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How Does Fitbit Calculate Calories Burned? How Accurate Is It?


I’ve investigated Fitbit smartwatches and fitness trackers long enough to know they can track a ton of stats with precision. That includes telling you exactly how much calories you burn. So how does Fitbit calculate calories burned?

Fitbit calculates calories burned using combination of your Basal Metabolic Rate and your activity data. Some models have built-in heart rate monitors, which can be quite helpful in determining calories burned during exercises. Fitbit then gives an estimate of calories you burned for the day.

Being able to see how much calories you burn can motivate you to work smarter towards becoming healthy, especially if you’re currently trying to lose weight.

In this guide, I’ll dive deeper how Fitbit calculates calories, the types of calories the device shows, and give you some recommendations.

Let’s get stared. 

How Your Fitbit Calculates Calories Burned

Fitbit devices have evolved from simple step pedometers to innovative tech that can help you improve the quality of your health.

In addition to tracking the type of activities you do, they also give you an estimate of the calories you burn while working out.

But how does Fitbit calculate calories burned exactly?

Fitbit devices depends on four unique types of data to determine how much calories you burn every day. These are:

  • Basal Metabolic Rate
  • Heart Rate 
  • Daily Steps
  • Tracked Exercises

Let’s look at each metric, so you can learn more about why they’re significant for determining how much calories you burn.

1. Tracked Exercises

Your Fitbit device tracks exercises in two different ways.

The first option is the SmartTrack technology. Here, your smartwatch or tracker automatically determines the type of exercise for you and logs it in the app on your behalf.

However, the drawback with the SmartTrack is that you have to be on the same activity for at least 15 minutes for Fitbit to recognize and record the type of exercise.

The second option is the manual logging of the workout. In this case, you have to log in to the app, enter details of the type of workout you’d like to track, and save the details. 

Whether you log exercise type manually or let the SmartTrack technology do it for you, Fitbit will end up collecting sufficient exercise data to determine how much calories you burn.

Of course, your daily activities will vary from time to time throughout the day, but Fitbit will still track calories burned in the process and add to your daily total.

2. Heart Rate

Fitbit can’t track blood pressure because they don’t have inflatable cuffs, and they aren’t smart enough to measure breathing rates.

However, latest models, such as Charge 5, Luxe, Sense, and Charge 4, have improved sensors that can read your heart rate and synchronize the data to your account.

Then, the app will use the heart rate data to calculate an estimate of the total calorie you’ve burned overall. 

Expect Fitbit to show that you’re burning calories at a slower rate if your HR is slow, whereas a higher heart rate reading signifies faster metabolism.

3. Basal Metabolic Rate

Popularly shortened as BMR, your basal metabolic rate is a numerical estimate of the amount of energy used while you’re at rest.

When your body is at rest, it means you aren’t engaging in intense activities such as running and lifting weights.

Interestingly, your Fitbit device uses the information you provided when filling out your profile in the app to determine your BMR. In addition to your height, age, weight, and gender, Fitbit will use heart rate, breathing rate, and blood pressure for the same. 

Keep in mind that the BMR data that Fitbit gets isn’t 100% accurate. What you get as your basal metabolic rate based on the data collected is just a rough estimate.

Still, the data is significant enough to help you understand just how much calories your body potentially burns when you’re not overly active.

4. Daily Steps

Another metric that Fitbit uses to determine how much calories your body burns is your step.

Every smartwatch and fitness tracker model that Fitbit has ever built can track every day steps.

Fitbit has refined the steps tracker over the years to make it smart enough to not only determine how many steps you feed the device every day but also detect when you don’t move.

More importantly, Fitbit uses your overall step count to give you an estimate of the total amount of calories burned during the day.

Unlike Samsung Health, Fitbit recommend walking 10,000 steps per day. Expect to burn 30 to 40 calories per 1,000 steps, which approximates to 300 to 400 calories per day if you walk the 10,000 steps.

3 Best Fitbit for Calorie Tracking

Fitbit devices are great, and you’ll love them because they deliver results exactly as advertised. The ones I recommend for calorie tracking are: 

These Fitbits are the latest models, so you can expect the estimate of the calories burned to be more reliable unlike what you’d get from older models.

How Accurate is Fitbit Calorie Burned?

Smartwatches and fitness trackers aren’t robust enough to guarantee 100% accurate results for the metrics they measure – although I wish they were.

So instead of assuring you that you’ll get precise results all the time, wearable brands make it clear that some stats are pure estimates, and you should treat them as such.

So how accurate is the calorie count by Fitbit?

Fitbit calories burned won’t be consistent all the time. Expect the results to change depending on the type and intensity of exercise, heart rate variability, activity level, weigh, and wrist placement.

  • Weight: How heavy you’re can influence the accuracy of Fitbit calories burned, with the possibility of getting wrong results if you fall outside certain weight range.
  • Heart Rate Variability: Because it varies from person to person, Fitbit can’t give exact results on calories burned because the results could be misleading.
  • Wrist Placement: As long as you wear your Fitbit on the non-dominant wrist, the heart rate sensor will read your pulse rate accordingly and give you reliable estimates of calories burned.
  • Activity Level: You’ll get an accurate estimate of the calories burned for moderate to vigorous workouts.
  • Workout Intensity: Fitbit might overestimate calories burned for more intense activities and underestimate results for low intense activities such as walking.

Even weather conditions can affect how much calories you burn. For instance, your BMR increases in warmer weather, causing your body to burn more calories than it would in cold weather with the same level of workout intensity.

Given the fluctuation of these results, Fitbit can only give you an estimate of the calories you burn than the actual figure.

And having improved its technology, with Fitbit Charge 5, Luxe, Sense, Charge 4 and Versa 3 more robust and reliable than the models that appeared first, you can expect the estimation to be more accurate, with an under or overestimation of not more than 4%.

Frequently Asked Questions

1. What Does Over Budget Mean on Fitbit?

Over budget on Fitbit means that you’ve eaten more calories than your body burned. You can use this information to optimize your workout and activity habits with your diet, so you can have a plan that allows you to burn more calories than you consume.

2. What Should My Fitbit Calories Burned Goal Be?

You should set a goal to burn at least 400 calories within a 24-hour period. You do have to work out to get your body to burn calories, so a mix of light, moderate, and high intense activities should help you to hit your target.

3. What Calories Does Fitbit Track?

Your Fitbit device tracks your basal metabolic rate (BMR) calories and the calories you burn when working out.

These two types of calories do form the majority of what your oy burns on a daily basis.

4. How Do I Improve Fitbit Calories Burned Accuracy?

You can improve the accuracy of your Fitbit’s calorie count by wearing the tracker on your non-dominant wrist and keeping it snug.

In addition to making sure that you update your current weight in the Fitbit app, you should also engage in light to vigorous activity on a regular basis.


I need you to understand that activity and fitness trackers aren’t perfect. Even Fitbit, despite being a household name in the niche, is yet to elevate its tracking technology to a point where its entities are 100% accurate.

But as much as Fitbit can’t calculate the exactly number of calories burned per day per the 10,000 recommended steps, you do get estimates with slight percentages error in estimation. And that means you can rely on the data to make more informed health and fitness goals. 

And don’t worry if Fitbit under or overestimates the calories you burn. The calories you burn with the help of the device are just an estimate that won’t be 100% precise.

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Michael Jonathan

Michael Jonathan is the brainchild of Apelo Studio. He loves talking about wearable devices, and he is passionate about helping you push your wearable device to its limits. His creativity and ability to tear electric components apart and put them back together makes him an incredible troubleshooter and blogger.

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