How Accurate is Your Apple Watch TDEE and Other Fitness Trackers?

It has never been easier to track exercise and calorie burn using your Apple Watch, wearable fitness trackers, or even your smartphone.

But, can the data from your Apple Watch or Fitbit be trusted to establish an accurate TDEE (Total Daily Energy Expenditure)?

Establishing the most accurate estimation of your TDEE is the best starting point to use when counting macros or doing Flexible Dieting IIFYM. However, estimating your exercise calorie burn is perhaps the trickiest part of the calculation.

Tested Accuracy of Apple Watch and Fitness Trackers

Fitness trackers like an Apple Watch and smartphones use your movement as well as heart rate to estimate how many calories you burn from an activity.

However, it has been proven time and again by investigative reporting that these devices are often inaccurate and can even overestimate your calorie burn by as much as double!

There’s more to measuring calorie burn than tracking movement and/or heart rate so sometimes the Apple Watch just can’t accurately measure calorie burn. Newer versions of Apple Watch are better than older versions when they just tracked movement and not also heart rate. 

If we look at a trusted exercise database like the one found on FreeDieting.com, we can see the difference in calorie burn an exercise like walking can have.

Example: Here we have a 165 lb, 5’5″ woman who walks for an hour. Here are just some of the different calorie burn scenarios that could result:

calorie burn for different types of walking

Crazy, right?! It ranges from a burn of 126 to as much as 618! Most step trackers can’t possibly tell the difference between different types of “steps” and even heart rate isn’t a great indication.

Instead of counting steps and using that information to factor your TDEE, you should be tracking specific types of exercise and if walking, this includes three factors; distance, speed, and elevation change.

If you don’t do this then you may find yourself extremely frustrated as to why you aren’t losing weight with counting macros or IIFYM or another type of dieting.

Another Example:

Let’s say your maintenance TDEE is 1800 calories.

We then deduct 20% for a safe weight loss calorie deficit which brings your TDEE to 1540 calories.

Your Apple Watch is telling you that you burned 500 calories with your steps throughout the day and you add that to your TDEE for a total of 2040 calories.

In reality, your casual walking throughout the day only burned 200 calories. This means your true exercise adjusted weight loss TDEE is 1740 calories.

This makes a huge difference in the rate of which you’ll see results.

Why? There are a few reasons, but the biggest one is the (often overlooked) concept of exercise conditioning.

exercise conditioning and fitness trackers like Apple Watch

Exercise Conditioning and Apple Watch Devices?

Exercise conditioning is your body’s ability to adapt and become more efficient when performing the same exercise. This is another reason your Apple Watch may not be as accurate as it needs to be.

Example:

Let’s say a person decides to start running a mile each day.

  • The first day the person runs a mile, they feel like they are about to die.
  • The second day, they feel a little less like death at the end of the mile.
  • The third day the mile gets a little easier to run.
  • By the end of a couple of weeks, running a mile isn’t a hard task at all.


The body has adapted to the exercise by becoming more efficient; The lungs have adapted, the heart has adapted, and the runner’s muscles have adapted.

Unfortunately, the number of calories burned from running a mile has also decreased as the body adapted. An Apple Watch and other fitness trackers can’t adjust for this.

There has been some research into this concept and one such review of research found marked muscle adaptations responsible for less energy consumption. 1

Another study showed a decrease in energy expenditure among 43% of the participants who used exercise to lose weight after a period of time. 2

While it’s hard to pinpoint the exact amount of calorie burn decrease after doing the same exercise over and over again, we do know it’s less.

Why This is a Problem?

If you’ve calculated your TDEE based on walking 3 miles a day on a treadmill or working out for an hour at the gym, you may be overestimating your calorie burn if you’ve been doing that same exercise for awhile.

This can slow your results and even possibly keep you from experiencing results with flexible dieting if your estimation is too far off.

How to Prevent Exercise Conditioning and Make Your Apple Watch More Accurate.

You can prevent exercise conditioning and therefore make your Apple Watch more accurately estimate your TDEE by regularly switching up your exercise routine. Here are some examples:

  • Increase the distance you run/walk periodically.
  • Increase the speed you run/walk.
  • Change the course you run/walk to include more uphills.
  • Adjust the incline/speed of your treadmill regularly.
  • Regularly increase the weight you are lifting.
  • Regularly increase the number of reps you are doing when weight training.

You probably get the idea. Keep your body guessing and don’t allow it to fully adapt to what you are doing. Keep pushing yourself!

Establishing an accurate TDEE is vital if you want to get the most out of counting macros. Understanding how exercise conditioning plays a factor in this and the limitations of fitness trackers like an Apple Watch will help keep you from frustrating plateaus.

By accounting for exercise conditioning as well as double-checking Apple Watch with other tools, you’ll be well on your way to success with counting macros.

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    References:

  • Holloszy, John O., and Edward F. Coyle. “Adaptations of skeletal muscle to endurance exercise and their metabolic consequences.” Journal of applied physiology 56.4 (1984): 831-838. link
  • Melanson, E. L., Keadle, S. K., Donnelly, J. E., Braun, B., & King, N. A. (2013). Resistance to exercise-induced weight loss: compensatory behavioral adaptations. Medicine and science in sports and exercise, 45(8), 1600. link
Ted Kallmyer is an ISSA certified Specialist in Fitness Nutrition and is our lead macro coach. If you need help reaching your weight loss/fitness goals see our personal coaching options.
Last Updated: September 12, 2019

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