How accurate are fitness trackers and smart devices?

Is your fitness tracker lying to you?

Fitness trackers monitor our every move, from steps taken to calories burned, and even provide data on the quality of our sleep. But how reliable are these measurements, and can we truly trust them to make informed decisions about our health and fitness?

Fitness trackers have become increasingly popular over the past few years, with more people turning to them to monitor their daily activity levels. Whether you're an athlete, a fitness enthusiast, or just looking to improve your overall health, these devices promise to help you track your progress and stay motivated.

However, recent studies have shown that not all activity trackers are created equal, and many of them may not be as accurate as we think when it comes to counting steps - which is something most modern trackers use as a baseline for their monitoring.

How do fitness trackers work?

Most modern fitness trackers can be told apart by what they measure. Some are accelerometers, others are heart rate monitors, and some combine both functions.

Accelerometers determine your body’s movement to estimate your energy expenditure, making use of electromagnetic sensors to detect motion. The tracker then interprets this information using an algorithm that trains the device over time to recognize what a step is and when you take one.

Trackers that measure your heart rate will use predetermined equations based on age, height, gender, weight, and activity levels, to estimate calorie expenditure. These types of trackers normally have a green LED light aimed at your wrist, which they use to measure your blood volume - the faster your heart beats, the more volume the light detects, the slower your heart beats, the less volume it detects, which is how the tracker is able to calculate your heart rate.


The Problem with Fitness Trackers

Modern fitness trackers use algorithms that were developed based on studies involving participants in their 20s, mainly focusing on normal walking patterns. This means that if you don't walk in a typical way, the tracker might not accurately count your steps. For instance, if you walk with an irregular gait, limp, shuffle, or don't swing your arm, the tracker might miss counting some of your steps.

This exact issue was highlighted by a study and systematic review that investigated Fitbit wearable technology. The study revealed that Fitbit fitness trackers often miscounted steps, particularly in older adults. About 25% of the time, Fitbit devices undercounted steps compared to other tracking methods. Additionally, when participants walked or jogged normally, these devices failed to count around 50% of the steps when compared to observed steps. When used outside of controlled laboratory conditions, the trackers also over-counted steps by about 35%.

The Challenge of Tracking Steps

The familiar goal of achieving 10,000 steps a day has become a universal fitness benchmark, even though this goal is not based on any scientific research. Recently, however, a study has shown that walking just 4,000 steps a day could significantly lower your risk of dying from any cause.

No matter what your daily step goal is, it won’t matter if you cannot trust that every step you take is being accurately counted.

In general, fitness trackers do a decent job of counting steps for most people, but certain factors can throw their accuracy off course. People who walk slowly or have a unique walking gait might find their steps are being undercounted. 

While your fitness tracker may provide step counts that are generally reliable, discrepancies tend to become apparent when you cross-reference the data from different trackers or even compare it with your smartphone's estimate. Interestingly, clip-on pedometers, which are meant to be worn on the hip, often provide more accurate step counts, suggesting that the placement of the device plays a crucial role.

Most modern fitness trackers are meant to be worn snugly on your wrist, just above the wrist bone. However, this way of wearing your tracker introduces a new challenge – extraneous movements that aren't related to physical activity. Wrist-worn devices might pick up movements like typing, gesturing, or even clapping, inaccurately inflating your overall activity count. Even if you wear the tracker on your non-dominant wrist, it's bound to register various hand movements throughout the day, mistaking them for steps taken.


Read more: Step counters vs smart devices: what is more accurate?


How to Choose an Accurate Fitness Tracker?

Given the unpredictable accuracy of fitness trackers, choosing the right device is not as easy as it may seem. Before you buy your next fitness tracker, consider the following points:

Compatibility with Your Phone

The first step is to ensure that the fitness tracker you're considering is compatible with your smartphone. For instance, the Apple Watch is an excellent choice for iPhone users, but if you're using a different brand of smartphone, it won’t do much for you.


Fitness trackers come with a range of features, from basic step counting to more advanced functions like sleep tracking and smartwatch capabilities. You should assess your needs – do you want a simple activity tracker or a device that also acts as a smartwatch?

Heart Rate

The presence of a heart rate sensor significantly enhances the accuracy of a fitness tracker, especially in estimating energy expenditure. Devices that employ accelerometry alone tend to be less accurate in this regard. Opt for a model with a heart rate sensor to ensure better results, especially if you walk slowly, use walking aids, or have an unusual walking gait.


Budget plays a role in any purchase decision. The good news is that even the more affordable fitness trackers with heart rate sensors can offer accurate measurements for most users. Pricier options might have additional features, but they might not necessarily provide significantly better accuracy.


The World Health Organization recommends a minimum of 150 minutes of moderate physical activity per week for adults, highlighting the importance of accurate activity tracking. The safest choice for you, if all you are looking to accurately monitor is your step count and how many steps you take in any given day, would be a standard clip-on pedometer, worn at the hip or inside your pocket for the best results.

Should You Invest in a Fitness Tracker?

When it comes to fitness trackers, accuracy is a complex issue. While these devices might not provide pinpoint precision, they can serve as valuable tools for motivation and general activity tracking.

If you're looking for a reliable step count, clip-on devices or even your smartphone might offer more accurate results than wrist-worn trackers. However, the integration of heart rate sensors has brought about improvements, especially in estimating energy expenditure.

As technology continues to advance, fitness trackers are likely to become more accurate over time. Companies are investing substantial resources in refining algorithms and enhancing sensor technology. But for now, it's essential to be aware of the limitations of these devices and use them as aids rather than definitive measurements.

Whether a fitness tracker is "worth it" depends on your goals and expectations. For tracking steps, they can be beneficial, but for precise energy expenditure data, you might want to consider alternative methods or consult with fitness professionals.

In the ever-evolving landscape of health and fitness technology, the most accurate tracking tool remains your own dedication to leading an active lifestyle. While fitness trackers can provide insights and motivation, the true measure of success lies in the steps you take, the miles you cover, and the moments of active living you incorporate into your daily routine.