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16 December 2020

How we test fitness trackers

Pounding the pavements, testing battery life and even checking for privacy and security – we go the extra mile to help you find the best fitness trackers
Christina Woodger

In-depth Which? tests put fitness trackers through a wide range of real-world scenarios to find out exactly how capable they are.

We only recommend fitness trackers that are comfortable to wear, easy to use, and accurate at tracking your fitness day in, day out. 

Fitness trackers from all the big brands, including Fitbit, Garmin, Huawei, Samsung and Polar go through a raft of tests in and out of our lab. The best trackers provide in-depth and accurate data on the device or an easy-to-use app, as well as helpful tools for motivation. They'll be comfortable to wear, and have a range of useful features. The worst we've found will overstate or understate steps and distance, struggle to measure your heart rate and lack useful features.

Each fitness tracker is tested in different scenarios to find out how they perform – from day-to-day activities to exercise. We put them through several rounds of testing too, so we can be sure our fitness tracker reviews can reliably answer your key questions, including:

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How accurately does a fitness tracker capture steps?

'Walking is simple, free and one of the easiest ways to get more active, lose weight and become healthier,' says the NHS. 

Whether you're specifically going for a walk, you're trying to incorporate more walking into your daily routines (walking to work in the morning, for example), or milling about the house, a fitness tracker could help you keep track of how many steps you clock up across the day. 10,000 steps is a popular daily target, but most fitness trackers will allow you to set a personalised goal. 

But fitness trackers can often miscalculate steps, wrongly registering any movement of your hand as a step or failing to register genuine steps. 

Our testers wear each fitness tracker on a 10-minute run and a 10-minute walk, and while carrying out a range of household activities, such as:

  • sitting reading a magazine
  • loading and unloading a dishwasher
  • sweeping the floor
  • going up and down stairs
  • carrying shopping bags

We compare the data from the fitness tracker to that from a trusted reference step-counter. 

Consistency is just as important as accuracy. If a tracker is accurate on some days but not on others, you won’t know whether you’re improving. So we repeat our walking test to see if the trackers consistently overstate, understate or hit the accuracy mark.  

How well does it track sports and exercise? And how well does it track heart rate?

Steps are important, but modern fitness trackers are capable of far more advanced tracking. 

If you're a runner looking to track the length of your run, we've got you covered. Whether the fitness tracker is relying on GPS to track distance, or whether it's relying on steps, we check if the fitness tracker can tell us correctly how far you've travelled. We take each fitness tracker on routes of known distances (both walking and running), including open sky areas and woodland areas to add the challenge of potential loss of GPS signal. 

More and more fitness trackers now measure heart rate. We test how accurately a fitness tracker measures heart rate during high-intensity running and while resting. If the fitness tracker gives no heart-rate data, or abnormal heart-rate data, we take a second reading. We use chest belts to compare the results – these use an electrical measurement method that is known to be more reliable, so we know we can trust their data. 

Can a fitness tracker help me exercise more and stay motivated?

The best fitness trackers are easy to use and offer motivational tools to help keep you engaged, such as customisable goals, online competitions against friends, ‘badges’ that you can earn and daily and weekly or monthly workout summaries. Some are clunky and hard to navigate, don't offer much in the way of motivation, or send you so many reminders to get moving that you feel nagged and hassled. 

Our testers spend weeks getting stuck into using each tracker and accompanying phone app. Our reviews can tell you how easy it is to navigate and customise, and its ability to keep you interested. 

Is it comfortable and will I want to wear it?

A fitness tracker could be super-accurate, but if it rubs your skin, digs into your arm or is just plain heavy and ugly, you’re not going to wear it.

You can’t tell from looking at an activity tracker in the box or in a photo what it will be like to wear. So our male and female testers rate each tracker for how comfy it is to wear for sports and daily life. We'll tell you in the reviews if it's likely to overwhelm a small wrist. 

Should I buy it?

Each of our tests makes an impact on our overall test score – the overall percentage score we award to each fitness tracker on test.

Some factors are more important than others, so we weight each result differently to ensure that the fitness tracker features you’re likely to use most are the ones that contribute the highest proportions to the total test score. 

The scoring breakdown is slightly different for fitness trackers and smartwatches, reflecting the fact that, if staying connected was your primary concern, you'd opt for a smartwatch rather than a fitness tracker. 

A fitness tracker needs to score at least 70% in our tests to become a Best Buy. Smartwatches need 73% to be labelled a Best Buy. Fitness trackers and smartwatches that score 45% or less are Don’t Buys.

Fitness trackers score breakdown

  • 45% fitness
  • 20% ease of use
  • 10% app
  • 10% battery
  • 5% smart functionality
  • 5% build quality
  • 5% features

Join Which? to access all our in-depth fitness and activity tracker reviews. Already a member? Log in to find your new fitness and activity tracker.

View all Fitness trackers