How Accurate are Fitbit Calories Burned?

Last Updated on August 14, 2021 by Michael Brockbank

The Fitbit Charge 4 is one of my most utilized pieces of equipment for losing weight. Mostly, that’s because it’s strapped to my wrist except when I charge it. But how accurate is the data for Fitbit calories burned?

That really depends on the individual. As everyone is different with a unique physiology, there could be a vast difference in calorie burn from one person to the next.

However, I’ve found that the data collected by Fitbit for calories burned to be quite accurate according to my physiology.

That is as long as I maintain a good diet. Foods rich in carbs will take more effort to burn.

How I Measure Fitbit Calories Burned

To figure out how accurate the Fibit records calories burned, I set up a case study for myself over the span of a month. I wish I would have thought to blog about the experience, but, here we are.

At any rate, this is how I discovered my own personal averages. Now remember, everyone is going to have different results. There are just too many variables to say with absolute certainty how many calories you’ll burn while being active.

Things such as metabolic rate, sex, height, weight, muscle density, and more all play a role in how well you burn calories.

How Calories Burned are Measured by the Fitbit

First, let’s understand how the Fitbit measures the calories you burn. While there are a few algorithmic adjustments the software makes, it basically gets this information from your heart rate and range of motion.

The more active you are, the more frequently your heart beats. This is to supply oxygen to various muscle groups. The Fitbit also detects physical movement from sensors within the watch.

Then, it compares this information to the results of the average human to get an idea of how many calories you burn.

Of course, there are a lot of things that can cause your heart rate to jump without being physically active. For instance, I slid right through a stop sign on black ice once while driving. Needless to say, you could see the Fitbit report of when my heart rate jumped up.

In the grand scheme of things, though, monitoring your heart rate and motion is a good indicator for detecting physical activity.

Remember, the information is based on human averages. Because every person is different, no fitness tracker will ever be absolutely accurate.

1. Use a Spreadsheet

Ah yes, here we go with more spreadsheets. I think I like them way too much. But, a spreadsheet is a good method for keeping track of any kind of data.

When setting up the spreadsheet, create columns for tracking:

  • Weight
    How much did you weigh this morning?
  • Calories in for the day
    How many calories worth of food did you eat for the entire day? I use MyFitnessPal to track everything I eat.
  • The number of Fitbit calories you burned
    How many calories does the Fitbit say you burned? It’s best if you enter this number the next day. This is because you’ll burn calories simply by being alive. And the Fitbit will reset at midnight.
  • Calorie deficit
    This is your calories burned minus your intake. If you’re trying to lose weight, you want the burn to be higher than what you ate.
  • Est. Weight Loss
    The estimated weight loss is your calorie deficit / 3500. Why 3500? Because it’s believed that there are 3500 calories per pound of weight. Of course, this is based on averages like everything else. 

So, your spreadsheet will begin looking similar to this:

WeightCalories InCalories OutDeficitEst Loss (lbs)
     

2. Daily Weigh-ins

I’m usually not a big fan of daily weigh-ins, especially if you’re trying to lose weight. There is a lot that can cause your weight to fluctuate from one day to the next.

And it can be quite discouraging if you put in a lot of effort yesterday only for the scale to say there’s no change today.

But for all intents and purposes for finding a baseline for calorie burn, it works fairly well.

The first thing I did in the morning was weigh myself naked on the scale. This way, I can prevent various clothing skewing results from one day to the next.

WeightCalories InCalories OutDeficitEst Loss (lbs)
225.6    

Keep in mind, if you’re following along to determine if your Fitbit shows calories burned with accuracy, you’ll have to conduct this experiment for several weeks.

This is because of those fluctuations I was talking about before. Too many things can alter daily results. So, you’ll want to get a baseline average over a long period of time.

3. Measure Calories In

To measure the amount of calories I eat on any given day, I use MyFitnessPal. It’s a free food-tracking app that works well whether you’re using a phone or your computer’s web browser.

You’ll need to track every single morsel you put into your body. At the end of the day, you can add the total calories to the spreadsheet.

WeightCalories InCalories OutDeficitEst Loss (lbs)
225.61250   

Most products have a label showing calorie count. And in reality, these are not absolute numbers either. But, they do give you a good idea about how much you’re consuming.

4. Measure Calories Out

When it comes to the Fitbit, the number of calories burned is better added to the spreadsheet the next day. This is because you’ll continue to burn calories just by being alive. And these “living” calories are added to the total each day.

So, the next morning, I would enter my “calories out” for that respective day.

WeightCalories InCalories OutDeficitEst Loss (lbs)
225.612503550  

As you can see from the above example, I would have burned more than twice what I consumed. In fact, this happens often when I stick to my Net 600 Calorie Diet.

5. Calculate Estimated Weight Loss

Lastly, I calculate the deficit in calories to give me a rough estimate of how much weight I lost that particular day. Then, I would compare the estimates to what the scale actually records.

So, the spreadsheet would look like this:

WeightCalories InCalories OutDeficitEst Loss (lbs)
225.61250355023000.67

Statistically, my weight starting the next day should be around 224.9. That’s because I take my weight from the day before and subtract it from the estimated loss.

But, what if it’s not? That’s why you’ll need to record everything for several weeks to get an accurate baseline for yourself. Remember, your weight can fluctuate wildly depending on a slew of unique factors.

However, I’ve found that on weeks when I maintained a good and balanced diet, the estimated weight I lost according to Fitbit data was near-exact what I actually lost.

My Personal Average Per Pound of Weight Loss

After crunching the numbers, I found that I can lose one pound for every 3,467 calories the Fitbit says I burn. This is pretty close to the average of 3500 that experts say equals one pound of fat.

In fact, I’m debating on doing this study again and doing a live blog post that updates when I enter data. This way, you can see how I go about recording everything.

At any rate, everyone is going to be different. But, thanks to the extensive data I collected over several weeks, I found the Fitbit to record calories burned with a high degree of accuracy.

Calories In are Not Always the Same

Now comes one of the most important parts of this little experiment. Not all calories are created equal. Some foods you eat will be loaded high with carbs while others will consist mostly of proteins.

How your body burns all of these things will be different from anyone else. This is another reason why I like using MyFitnessPal. I can look back and see what foods are hindering my performance.

For instance, while doing the keto experiment, I often have days when I’ll lose two pounds. This has more to do with transitioning my body to use fat instead of carbs for energy.

So even though the Fitbit Charge 4 calories say I burned 0.46 pounds, I actually lost far more. This is because what you eat plays a major role in how much you can lose.

Anyway, when I conducted the case study on myself a couple of years ago, I ate as I normally would. This usually includes more carbs because I have a sweet tooth.

Just keep in mind that foods have a vastly different nutritional value when it comes to the calorie count. For example, 2000 calories of cupcakes is going to be harder to burn than 2000 calories worth of vegetables.

That’s a lot of veggies, actually. I don’t know if I could eat 2000 calories worth of vegetables in one day. That would be like eating 45.5 medium-sized onions.

Again, that’s because of the carb count and depends on how physically active you are.

Use Fitbit Calories Burned as a Guide

Let’s say you don’t want to use the data-dork method of tracking Fitbit calories burned for accuracy in a spreadsheet. No matter what, the sensors will give you an idea about how active you are in general.

And this is perhaps one of the most vital keys to losing weight of any kind…physical activity.

The more active you are, the more you burn. And as the Fitbit records heart rate and motion, it can guide you to coming up with exercise routines to maximize your efforts.

It’s all about working up a sweat.

Everyone is Unique

The most important thing to keep in mind regardless of diet or exercise routine is that everyone is different. What works well for one, may not work all that well for another.

Using something like Fitbit for tracking calories burned can help you as a guide, but it’s not an absolute figure. Like I said, no fitness tracker is 100% accurate according to your unique physiology.

Use these things as more of a way to show you what you need to work on. Find your own baselines, limits, and measurements.

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Michael Brockbank

Since 2015, Michael has put in the effort to lose more than 80 pounds by gamifying fitness and eating proper portion sizes. He conducts extensive research into various health and fitness products to provide the best answers possible according to his own experience and knowledge.

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