The Best Fitness Trackers

How We Tested Our Top Picks

The step-counting test

We strapped on each device and took them out for a spin around the block, counting out exactly 300 steps each time (0.149 miles according to Google Maps, though most of these devices only log distance out to two decimal points, so we rounded up to 0.15 miles). We then recorded the number of steps logged by each device and repeated the test three times.

We were less interested in which devices nailed the 300-step mark every time and more interested in their consistency across tests.

In the above chart, solid bars represent average scores; barbell lines depict the range of results across three tests.

As you can see, none of the top contenders were perfectly accurate in terms of step counting. A few of them were fairly consistent, however, which is represented by the standard deviation, or how far apart the numbers were from one another. The TomTom Spark 3 and iFit Link fared the best in terms of consistency with a standard deviation of 3.51 and 7.21 steps, respectively.

The worst offender was the Fitbit Flex 2, which trended consistently low, logging well under 300 steps every time, with a standard deviation of 16.80 steps. That adds up to only a few yards over the course of just 300 steps, but expand that discrepancy out over the course of a whole day, and your step count may very well be off by more than a mile come dinner time.

Keeping tabs on calorie burn

In our calorie-burn test, all our contenders recorded higher on average than the benchmark, which was recorded using a more accurate EKG chest strap heart rate monitor. Only the TomTom Spark 3, Fitbit Surge, and Garmin Vivofit 3 were within 10 calories.

The Fitbit Flex 2 was the worst offender by far, logging as many as 43 more calories than the benchmark reading. This could present a problem if you’re actively relying on your device to help you determine your daily calorie allowance (e.g., through the Fitbit app or Garmin’s integration with MyFitnessPal), no matter which of these devices you’re using.

If your tracker is off by just 10 percent on your daily calorie expenditure (and even the best of our contenders were), it could regularly make it seem like you can afford to eat a few hundred calories extra.

Ruling out false positives (aka counting only real steps)

Since humans do all kinds of physical activities throughout a given day that might look like steps to a fitness tracker, your device’s algorithms should be able to parse out movements like washing dishes, typing a strongly worded email, or vigorously slamming down a cheeseburger, without misidentifying them as actual, calorie-burning steps.

With few exceptions, they all logged steps when they weren’t supposed to, though some were much further from the mark than others. This means that all of the above activities might actually get you credit toward your fitness goals (including enthusiastic gluttony), which seems to be a pretty big flaw in the whole fitness tracker concept.

For our first attempt at psyching out each device, we stood in place and swung our arms back and forth 100 times. The idea: Simulate walking without any actual forward movement. Ideally, the trackers would log zero steps, since we didn’t actually move from a static position. This, it turns out, was giving them a little too much credit, as they all uniformly failed.

Each device counted over 100 steps, even when we hadn’t moved an inch. Then we did the exact inverse, walking 100 steps without swinging our arms. This simulated doing an activity like pushing a grocery cart or a stroller, where a walker wouldn’t necessarily swing their arms. Every device was off by at least 20 to 30 steps.

Heart rate monitoring

By using an onboard heart rate sensor, devices like the iFit Axis, TomTom Touch, and Fitbit Charge 2 can hypothetically give you much more accurate fitness data, especially calorie burn, by recording intensity and duration. This circumvents the issue of tracking actual movement to determine output and effort, opening up the full range of exercises for tracking, from spinning to sumo wrestling.

We used a half-mile run on an indoor track as our default exercise. We put each device through three sessions each, recording distance, calories, and heart rate, and then used a chest-worn heart-rate monitor as a benchmark for our heart rate and calorie-burn calculations.

On the whole, the fitness tracker readings performed quite poorly compared to the chest strap monitor. As a collective group, they were all off by an average of 19.5 beats per minute over the course of three separate tests.