top of page

Calories burned on your wrist tracker… are they accurate and should you rely on them?

The popularity of wearable devices to track workouts and other fitness and health data has been on a steady incline for a few years now and has no indication of slowing down.

Sales of wrist trackers between 2014 and 2015 doubled, whilst between 2019 and 2022 spending on wearable devices went from 46.19 billion US dollars to 93.86 billion dollars (4).

If we look at some of the figures from Fitbit (one of the market leaders and first to launch fitness wearables) over the past 4 years, the amount of users has been on a steady climb (2017: 25.4 million, 2018: 27.6 million, 2019: 29.6 million and 2020: 31 million) (1).

On Instagram, there will always be someone on your timeline feed showing how many calories they just burned in their workout.

The point of this article is not to demotivate you and tell you everything that you’re doing is wrong, it is to provide you with some useful information on the wearables and give you the tools to allow you to be sufficiently competent at monitoring your own health and fitness journey without the reliance on other things.

If you were to ask a well educated coach “are fitness wearables accurate for tracking the number of calories burned during a workout?” they will say NO!

Fitness trackers are not accurate, HOWEVER, they can be a good starting point. Please continue to read the rest of this article to see another more reliable tool you can add to your fitness toolkit…”

How do fitness trackers work?

Fitness trackers mainly use heart rate and sometimes other data points based on what you input (typically: Sex, weight, and age), to create an algorithm estimating the amount of work


Usually, the algorithm is designed by a very smart person in the physiology world. So they aren’t completely bad.

The Pros

Having something like a fitness watch can be very motivational and can make you more active. This can be due to the watch storing your data allowing you to see the progress being made. It also keeps you somewhat accountable for turning up to your workouts with something as simple as a notification, or simply because it has a live feed of physiological response to the exercise you are doing.

If you see you are burning more calories each session you will probably see that as you are making some obvious improvements.

Being objective data it's easily trackable. If you are on a training plan, either of your own or working with a coach, that data can inform training decisions based on the goal that you want to achieve.

The Cons

A meta-analysis study looked at 20 different wearable trackers, including all of the big dogs in the market. The study found that the trackers overestimated the number of calories spent during a workout by 28%-93% (3).

This means that if your watch said that you spent 500 calories during your workout, leading you to eat back those calories, that could be a difference of 140-465 calories more than you need. That difference of extra consumption potentially means your progress slows right down and/or completely stops.

Away from calories burned, some trackers offer other units of measure to try and quantify your energy levels or how you feel. These are still calculated using your HR and a preset algorithm, meaning it is often not a true representation of reality. What it cannot account for are extraneous variables such as caffeine or common (but difficult) life stressors that we experience through the days. The dreaded commute to and from work or dealing with stresses that come with having children can affect your stress levels, hormone levels and heart rate, therefore affecting how you may feel.

One huge problem often ignored is the bad relationship with food that can potentially develop when trying to eating back calories your app or tracker says have been spent. Honary and colleagues conducted a study looking at the potential risks around healthy eating and fitness app use and negative experience and behavior amongst teenagers and found that more than 50% of participants experienced some sort of negative experience when using the apps and/or devices (2).

Earning your food, burning the guilty cheat meal you just had or out exercising your diet are all terrible and unhealthy approaches to both exercise and diet. This sort of mentality is not healthy and can lead to serious consequences on a person's health and can all be prevented with education and understanding principles of exercise and a balanced diet and lifestyle.

An alternative solution and much more accurate:

Workout your Total Daily Energy Expenditure (TDEE).

I suggest you set out your next 2 weeks to

  • Weigh yourself every morning after you’ve been to the toilet and before you consume any food or water.

  • Track your food intake using either food labels and/or an app like MyFitnessPal.

If you have been eating the same amount of calories and doing the same amount of moving around for the 2 weeks set aside, and your weight has stayed the same, you have found your maintenance calories (the number of calories you need to stay at the same bodyweight.

In which case, you would then be able to work out your needed deficit to lose weight or surplus to put some weight on.

I would generally advise creating no more than a 15% surplus or deficit, to make it as smooth and as pleasant as possible.

For example, if you have worked out that your daily maintenance calories to be at 2000kcals, to create a deficit, would then reduce your calories by 300kcals and only eat around 1700kcals per day.

Yours always,

Luke :)

Please remember, these articles are always for advisory purposes only and we hold no responsibility for your actions taken. Before trying anything mentioned in anything in these articles, please remember to seek help from a medical professional.


1. BOA, 2021. Fitbit Revenue and Usage Statistics (2021). [online] Business of Apps. Available at: <> [Accessed 8 November 2021].

2. Honary, M., Bell, B., Clinch, S., Wild, S. and McNaney, R., 2019. Understanding the Role of Healthy Eating and Fitness Mobile Apps in the Formation of Maladaptive Eating and Exercise Behaviors in Young People. JMIR mHealth and uHealth, 7(6), p.e14239.

3. Shcherbina, A., Mattsson, C., Waggott, D., Salisbury, H., Christle, J., Hastie, T., Wheeler, M. and Ashley, E., 2017. Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort. Journal of Personalized Medicine, 7(2), p.3.

4. Statista, 2021. Wearable end-user spending worldwide 2021 | Statista. [online] Statista. Available at: <> [Accessed 8 November 2021].

69 views0 comments


bottom of page