Fitness trackers: what do they do, and why should I buy one?

Do you need sleep tracking? What does hitting 10,000 steps actually mean? What if you want to monitor for falls, work out your fitness age or track daily medication?

With so many features suiting different needs (and budgets), we’re here to help you figure out what you need most from a fitness tracker and answer the questions our readers are asking the most.

A fitness tracker is a band you wear around your wrist and are either bands (looking like a bracelet with a thin screen) or – more commonly as features improve – a watch with a larger display. While wearing it, the wearable monitors how many steps you take throughout the day and the calories you burn. 

More advanced fitness trackers can also keep an eye on how well you sleep and the types of exercise you participate in, as well as motion detectors to spot if you’ve had a fall or been in a car accident, or offering apps that can monitor hydration, medication or stress levels.

Many fitness trackers are capable of monitoring your heart rate throughout the day by shining light at your skin and reading your blood flow, and also track your exercise through built-in GPS (like the type you’d see on your smartphone).

Before we answer this question, it’s based on one assumption: you’d like to get to know your body better and get healthier. Without that goal, you’ll be bombarded with useless information – a fitness tracker alone can’t improve your wellbeing, but it can arm you with incredible knowledge.

Fitness trackers are a great way of tracking your daily activities and general health while being reasonably affordable compared to a smartwatch – although the line between a fitness tracker and smartwatch is blurring as the tech inside becomes more affordable and consumers demand more useful features.

It’s possible to use your smartphone to track walks and other activities, but a fitness tracker is more accurate and reliable as it sits on your wrist with one goal: to constantly keep an eye on your health, rather than checking messages, browsing the web and taking photos. 

Using a fitness tracker also means you don’t need to carry your smartphone with you at all times, and you can use your handset to view your health data in more detail at a time more convenient to you.

If you’re planning to go to the gym or walk more, a fitness tracker can monitor each activity you’re performing, providing insight into the calories you’ve burned and – with many fitness trackers – your heart rate during those activities, so you can get a true idea of how much harder you’re working.

Besides offering a more detailed view of your day, it can also monitor how well you sleep throughout the night. This includes looking at different sleep stages, such as REM or light sleep, and allows you to check the effects any alterations to your sleeping habits you might make, or spot trends that you might have missed (like the effect of alcohol or medication on your slumber).

Before buying a fitness tracker, knowing why you want one is helpful. Nearly all fitness trackers provide a daily step count and calories burned, but do you need more? 

If you want to run regularly, a fitness tracker with a built-in GPS is vital so you can see where you’ve travelled. It’s helpful to also have heart rate tracking to see how hard you’re actually running, as well as providing a more accurate calorie burn.

Similarly, if you plan on hitting the gym regularly, these features can help you work towards your goals more effectively. If you want something that will track your swims, we’d suggest looking at a dedicated fitness watch like those from Garmin or Apple, as they’re heavily water-resistant and have apps to properly show swim effort and length tracking, for instance.

If you just want a fitness tracker for sleep monitoring, we’d suggest going for something dedicated like the Withings Sleep Tracking Mat, rather than a band which might be uncomfortable to wear on your wrist initially.

The Sleep Tracking Mat is placed under the bed and is far more accurate at spotting your sleep stages – with useful nightly feedback. 

Ultimately, the amount of things you want to track – and track accurately – will define how much you should spend on a tracker… and how large it might be too.

Whatever your health and fitness goals might be, having duff information can hinder your progress. So just how accurate are fitness trackers? In summary, they aren’t perfect. But depending on what you want to measure, they can still be helpful.

When it comes to walking, the majority of wearables use motion sensors to record the number of steps we take. But there are several factors that can influence accuracy. One study from 2020 suggested that continuous walking tends to offer more accurate readings than intermittent movement. There are also issues with wrist-worn devices, which can sometimes mistake arm movements as steps. Ankle and hip worn devices are more accurate in this respect.

A more recent review of the research, conducted in 2022, highlighted significant variance between brands and models. The Fitbit Charge and Fitbit Charge HR were, “consistently shown to have a good accuracy for step counts”.

Overall, while a fitness tracker will offer you some insight into how many steps you’ve done, don’t assume the number is completely reliable.

Another popular metric fitness trackers offer is calorie burn. But once again, the evidence suggests that we shouldn’t be relying on these before telling us whether we can have a second helping of pudding. A study from 2019 stated that fitness trackers “did not show valid results concerning the estimation…of EE [energy expenditure]”. In other words, they weren’t accurate at estimating calories burnt, and indeed, both overestimated and underestimated energy expenditure. 

Another study in 2018 described the measurement accuracy of energy consumption as “inadequate”. Finally, a meta-analysis from 2020 in the British Journal of Sports Medicine found that devices, “showed variable accuracy depending on activity type” but if the tracker includes a heart rate monitor or heat sensor, this did improve accuracy. 

Calorie burn can be influenced by a wide range of different factors. So while it can be interesting to see how one day compares to another, don’t try to use your fitness tracker to gauge whether you are running a calorie deficit or not. It just isn’t reliable enough.

When it comes to monitoring your heart rate, the news is mixed. Some studies, such as this one from 2018, suggest that “mainstream devices are able to reliably measure heart rate”. This one from 2020 suggests that, “commonly used optical heart rate sensors…generally produce accurate heart rate readings irrespective of the age of the user”. But this is still caveated with the warning that “these devices have a tendency to produce erroneous, extreme readings”. So even when they are generally accurate, sometimes they aren’t. Which isn’t ideal.

Wrist worn heart rate measurements tend to be less accurate than readings taken via a chest strap. And there are other factors that can influence accuracy. For instance, as this study from the Journal of the American College of Cardiology shows, optical heart rate monitors, which use light to measure your pulse, points to, “a significant reduction in accuracy of heart rate measurement with wearable devices in darker-skinned individuals”.

And finally, are fitness trackers accurate when recording your sleep? As we suggested above, if sleep is your primary concern, then a sleep tracking mat is likely to deliver more comprehensive feedback. 

Because a fitness tracker is generally worn on your wrist, it relies on your heart rate and movement to decide whether you are asleep or not. Essentially, it’s making an educated guess. But if you simply lie very still, a fitness tracker may record this as sleep, even if you are wide awake counting sheep, reading a book, or watching a film. 

While it may give you an indication of how long you slept for, your fitness tracker cannot reliably tell you whether you were in light sleep, deep sleep, or REM sleep. And the information it does provide, is not especially accurate, as reported in this 2020 study.

After reading all that, you might be wondering what the point of a fitness tracker is if they aren’t completely accurate. Well, despite their flaws, there is robust evidence that suggests activity trackers can be very effective at improving physical activity at all ages. 

In other words, simply having a fitness tracker can encourage you to be more active, even if the data it’s showing you isn’t perfect. And they can still be useful for tracking your progress over an extended period of time, and keeping you motivated.

As we mentioned, there are two types of fitness tracker: band and watch. You might be drawn to the latter because of the larger, more visible display (and it often comes with a longer battery life) but they are more cumbersome.

For instance, Fitbit offers the Fitbit Inspire 3, which has a thin screen that provides just enough room to see the steps you take along with the time, your heart rate and other basic stats. It’s harder to view, is more basic, but costs less and is more discreet.

Alternatively, there’s the Fitbit Charge 5, which has a larger and clearer OLED display. OLED (which stands for Organic Light Emitting Diode) technology means that the screen is easier to see in all conditions, even if you’re out in bright sunlight. 

It’s bulkier though, being slightly wider than the Inspire 3. You can go even larger if you wanted, with something like the Garmin Forerunner 55 allowing you to start running with more performance metrics, monitor your daily stress levels and get a longer-lasting battery – all on a larger screen.

Besides considering if you want a wider wearable on your wrist or something more narrow, you also need to consider colour options. 

Most fitness trackers offer swappable bands, so you can try different colour schemes – although you’ll need to look to devices from the likes of Fitbit, Apple and Garmin to get a good suite of options.

Depending on the make, this can be as simple as buying a regular watch strap, but others may require you to buy a proprietary strap which can make things expensive.

We’re currently conducting our Exceptional testing on a range of fitness trackers that will matter to our readers, and until that’s complete we won’t offer the definitive view on what the very best fitness tracker is.

That said, if you’re wondering what the best fitness tracker is for you, then our writers have used and researched a great many options so can give you some tips to get started in your decision-making.

If you want something that’s slimmer and does it all, the Fitbit Luxe is a top choice. If it’s things like full health monitoring, fall detection, medication reminders and a full range of activity tracking, then the Apple Watch Series 7 (not the 8, which doesn’t offer enough of an upgrade) is our pick – although the Apple Watch SE is decent and cheaper if you’re on more of a budget.

For runners and swimmers, the Garmin Forerunner 55 is a relatively low-cost option that also offers things like stress tracking, respiration monitoring and sleep monitoring to boot.

And if you just want a budget model, brands like Huawei, Xiaomi and Amazfit offer a variety of features with great results too.

Once you buy a fitness tracker, you’ll need to pair it up with your smartphone. While you can check a lot of your stats and activity from the fitness tracker, the bulk of the information you’ll want to read is available through a relevant companion app. 

Almost all Android and iPhones are compatible with these apps. However, if your smartphone is quite old, double-check the manufacturer’s website to confirm that your phone is still compatible – or consider using an iPad to do your monitoring instead, if you happen to have a more modern device than your phone. 

Such apps tend to be free, but companies like Fitbit also offer a premium subscription that provides you with more advanced features and analysis. It’s optional to subscribe to such a service, but it can help you maintain or improve fitness, depending on your goal.

It’s also frequently possible to use apps like Map My Fitness with your fitness tracker, so you can track your progress through apps you’re already accustomed to.

The battery life of fitness trackers is far better than your phone or a smartwatch. For instance, the cheaper Honor Band 5 offers an estimated battery life of two weeks with the same kind of figure possible from the Amazfit Band 5. 

The popular Fitbit Inspire 2 and 3 offer around 10 days, while the Fitbit Charge 5 with its brighter screen, provides up to 7 days according to its manufacturer.

These figures are typically reasonably accurate for the most part. The number may dip if you have a particularly active week and find yourself frequently running, walking, or working out in some way, but it’s rarely a significant drop. Fitness trackers have chargers that plug in via your laptop’s USB port or a wall block that came with your smartphone or other electronics. 

Such chargers are usually proprietary ones that can only be used with that brand’s range rather than a regular USB cable. We’d suggest buying a second cable to side-step those frustrating moments when you want to workout or track your steps, only to find it’s out of charge.

Expect full recharging to take around 2 hours. If you want wireless charging, you’ll generally need to buy a smartwatch. 

Fitness trackers vary in cost substantially depending on what features you want, if you want a well-named brand, and if there happens to be a sale going on at the time. 

If you want basic features such as a pedometer, calorie tracking, and basic sleep monitoring, the cost can be as low as £20. That’s for a lesser-known brand and won’t come with a smartphone app (or not a very good one…), but it’ll do the job if you just want to get going and see an improvement.

Alternatively, pay up to £30 and you can own a fitness tracker from a more reputable company such as Honor or Amazfit and gain extras like heart rate monitoring and more expansive workout modes. 

Some fitness trackers in this price range include blood oxygen monitoring and 24/7 heart rate tracking, but they’re not as fully-featured or in-depth in their analysis as more expensive models. 

The most popular fitness tracker brand is Fitbit, which costs more than many competitors. The cheapest Fitbit is the Inspire 3, priced at £85, but you can often find it in a sale – and if you’re lucky, the slightly older Fitbit Inspire 2 can sometimes be found even cheaper. 

Such devices offer extra features like Active Zone Minutes that show how much you push yourself during a workout or walk. The Fitbit Inspire 3 also includes a daily readiness score so you can see at a glance if today is the day to work out or rest. 

Pricier still is the Fitbit Charge 5 at £170, providing a more smartwatch/fitness tracker hybrid style and an always-on display.

Clearly, there’s a lot to think about when choosing one of these devices. If you need a little help, here are five things to consider when buying a fitness tracker.