Top fitness trackers for 2021
Whether you’re looking for a simple activity tracker for monitoring steps and distance travelled, or you want one with more advanced features for running or swimming, Which? can help you find the best.
In the tables below we pick out some of the best wearables for a variety of activities, based on how they've fared in our tough test labs.
Best overall fitness trackers
The trackers below are great all-rounders. They should be able to handle a wide range of sports and activities, they tracked steps and distance with little error in our tests, and they're comfortable to wear.
Best fitness trackers for accurate step counting
Walking is a free, easy form of exercise. If you've tended to be quite sedentary in the past, then aiming for a daily step target can be a great way to get into exercise.
Every fitness or activity tracker will capture your steps. Many will let you know once you've met your target: 10,000 steps is a common one, but you can often customise this according to your level of fitness.
But not all trackers are equal when it comes to the accuracy of their tracking or the motivational tools they use to get you moving more.
We’ve found several fitness trackers that overstated or understated steps taken by more than 40% during everyday tasks, clocking up steps when our test participants were simply flipping the pages of a magazine. But it’s not all bad news, as we’ve also found lots of trackers that are strides ahead when it comes to accuracy – including the devices below.
These trackers aren't the absolute best on test (see the table above for those), but they're the best choice if your main criteria is step tracking. All of them score 5 stars for step count accuracy and are good overall models.
How we test for accurate step tracking
A pedometer is the most basic sensor, and it's one you’ll find in every fitness tracker or smartwatch for counting your steps.
We test how accurately fitness trackers count steps during household activities, including packing and unpacking the dishwasher, sweeping the floor, going up and down stairs and sitting reading a magazine.
We’ve tried out fitness trackers ranging in price from £12 to more than £200 and we've found both cheap and expensive models that struggle to track step count accurately. That can be because the accelerometer is too sensitive, and wrongly logs every wrist movement as a step.
Best fitness trackers with heart-rate monitors
A built-in heart-rate monitor is a useful feature and, if accurate, can help you track your active heart-rate zone (particularly useful if you’re looking to burn fat), and measure improvements in training. We’ve tested fitness watches and activity trackers with heart-rate monitors from brands including Fitbit, Garmin, Polar and Samsung, among others, but some devices have struggled in our tests. We've found wearables that are inaccurate by nearly 50% when measuring heart rate.
How do we test heart-rate tracking accuracy?
We test fitness trackers during low intensity exercise, high intensity running and cycling, and while resting, to see how accurately each tracker can measure heart rate.
Our testers wear chest belts, as reference devices, as these use an electrical measurement method that is known to be reliable. And we compare these results to those recorded by the wearable.
As with step-tracking, we see big differences in how accurately a fitness tracker can measure heart rate. We've seen a fair few - including cheap and pricey models - that are only accurate in certain scenarios: tracking accurately during high-intensity exercise but struggling during low intensity exercise or at rest, for example.
Best GPS fitness trackers for running
Not all trackers have built-in GPS. Many (particularly the cheaper ones) rely on your phone's GPS, while a few have no GPS functionality at all.
If you want to leave your smartphone at home while still tracking your distance and route using your wearable device, look for a tracker with built-in GPS. Trackers which measure distance using GPS tend to do so more accurately than those which measure it based on step count alone, although that isn't always the case. Bear in mind that GPS will be more of a drain on your battery.
How we test fitness trackers for distance accuracy
All fitness trackers are taken on runs and walks along routes of a known length, to see how accurately they can track your distance travelled. Our routes include woods with dense tree cover to really challenge GPS trackers.
Best waterproof fitness trackers for swimming
Not all fitness trackers can be used in the water. And those advertised as being pool-friendly don’t always give you much data.
But some can give you a more comprehensive picture of your swimming - tracking information such as number of lengths, pace, stroke rate, distance, duration and calories burned. Some can give you a SWOLF rating (a measure of your swimming efficiency) and some can automatically detect whether you're doing front crawl, breast stroke, butterfly or another common stroke. One we tried out even detected we were at the leisure centre based on GPS and asked if we wanted to begin a pool swim.
Be aware that, if you want to use a float at any point, to force yourself to use your legs, your device probably won't log your lengths, as you're not moving your arms. Also be aware that many devices can't give you heart-rate data in swim-mode. However, some can be paired with a heart-rate monitor chest strap.
Here are some of the most detailed fitness trackers for swimming that we've come across.
Water ratings explained
Water ratings are a confusing topic, and rating codes may mean different things depending on the type of device they are referring to. In the tables below we look at the different ratings, and what each one means in terms of how you can use your fitness tracker around and in water.
There are two main ways to find out what level of water protection or resistance your fitness tracker has. The first thing to look for is the Ingress Protection (IP) rating. These are set by the International Electrotechnical Commission (IEC), and refer to the protection provided by the casing of an electrical device in fresh water.
The first digit after the IP reflects the level of protection against solids, such as dust or grit. The second represents the protection against moisture. An IP code with an X in place of either number means the device hasn't been tested for that element. For example, a fitness tracker with a rating of IPX7 has been tested for moisture protection, but not dust.
|IP code||Level of protection|
|1 - 3||Protection against light rain|
|4 - 6||Splashproof|
|7||Protected from immersion in water with a depth of up to 1 metre for up to 30 minutes|
|8||Protected from continuous immersion in water with a depth of more than 1 metre|
The second is the water-pressure rating. These are standards set by the International Organisation for Standardisation (ISO). Pressure tests are measured in atmospheres (ATMs), and replicate the level of pressure at certain depths of water.
|Water ratings||Level of protection|
|1 ATM||Resistant to pressure equivalent to a depth of 10 metres. Splashproof, but not shower or swim proof.|
|3 ATM||Resistant to pressure equivalent to a depth of 30 metres. Splashproof and shower proof, and should be fine if accidentally submersed. Not designed for swimming.|
|5 ATM||Resistant to pressure equivalent to a depth of 50 metres. Splashproof, shower proof, can be worn swimming and snorkelling in shallow water.|
|10 ATM||Resistant to pressure equivalent to a depth of 100 metres. Splashproof, shower proof, swimming and snorkelling. Not designed for deep water diving or water sports.|
|20 ATM||Resistant to pressure equivalent to a depth of 200 metres. Splashproof, shower proof, swimming and snorkelling. Surface diving and watersports, but no deep-water diving.|
Fitness trackers to avoid
There’s a great selection of wearables in the tables on this page, but our tests have also uncovered products that are inaccurate, uncomfortable to wear, have a short battery life or are annoying to use in some other key way. These devices will soon end up getting shoved into a drawer and forgotten about. Don't pick one of the trackers in the table below.
Pricing, recommendations and test scores correct as of March 2021.
How we test fitness trackers
Our tests go the extra mile, using specialist lab equipment to check the accuracy of the tracking capabilities of each device. Our panel of users gets to grips with the trackers over a number of weeks, so that we can tell you how easy to use and comfortable to wear each device is too.