Skip to main content

Fitness trackers appear to be lousy calorie counters, but it’s not all bad news

1188184 autosave v1 fitness trackers
If you’ve been using your fitness tracker’s calorie measurements to shape your diet, then you’re not going to like what you’re about to read: The data is well off the mark.

That, at least, is the conclusion of a team of researchers at the Stanford University School of Medicine, which ran tests on seven wrist-worn devices that offer users a range of health-related measurements.

The researchers evaluated the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, and Samsung Gear S2 among a diverse group of volunteers, and published their findings this week. While many of the devices have been updated, retired, or even recalled, we can assume that many are still being used by the millions of people that bought them.

Looking at the team’s data, even the best performing device — the FitBit Surge — was way off the mark when counting burned calories, missing the real figure by 27 percent. The least accurate was the PulseOn, which was off by a whopping 93 percent.

“People are basing life decisions on the data provided by these devices,” Euan Ashley, a professor of cardiovascular medicine at Stanford and senior author of the research report, said in a release, adding that it can be hard for doctors to know how to respond to data offered by a patient with their own fitness tracker.

While the researchers couldn’t be certain as to why the energy expenditure data was so inaccurate, they noted that the devices each use proprietary algorithms for calculating such data. Anna Shcherbina, one of the report’s authors, commented that it’s “very hard to train an algorithm that would be accurate across a wide variety of people because energy expenditure is variable based on someone’s fitness level, height and weight, etc.”

But before you toss your tracker in the trash, you might like to know that the findings weren’t all bad. For example, it was discovered that six of the devices measured heart rate with an error rate of less than 5 percent, while Samsung’s Gear S2 device had an error rate of 6.8 percent. These more accurate measurements can be put down to the fact that such data is measured directly rather than by way of an algorithm.

Ashley concluded that for the devices tested, a user can have a fair amount of confidence in the heart rate data, adding that you’ll clearly want to be very wary about designing your diet on the basis of the calories-count readout.

“The heart rate measurements performed far better than we expected, but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me,” the researcher said.

We can certainly expect developments in software and technology to improve the accuracy of tracker data and look forward to seeing the results of additional research on more recently released — and future — fitness-focused devices.

Editors' Recommendations

Trevor Mogg
Contributing Editor
Not so many moons ago, Trevor moved from one tea-loving island nation that drives on the left (Britain) to another (Japan)…
Fitbit’s kid-friendly Ace 2 fitness tracker now available for pre-order
fitbit ace 2 fitness tracker for children on sale

Earlier this year, Fitbit introduced its Ace 2 fitness tracker, a wearable geared for children ages 6 and older. The device can track a child's daily activity and share that information with their parents.  Just in time for summer vacation, the Fitbit Ace 2 is now available for purchase.

A followup to the original Fitbit Ace, the Ace 2 comes in two different colors, Night Sky/Neon Yellow and Watermelon/Teal, but you can change the color with replaceable bands. The silicone bands are comfortable to wear and can be adjusted to accommodate a child's growing wrist. It is waterproof up to 50 meters, allowing kids to wear the tracker in the shower or for a dip in the pool.

Read more
The best cheap fitness trackers of 2019
Stay fit and save cash with these affordable fitness trackers

Although there are a variety of high-end fitness-tracking devices -- such as the Apple Watch Series 4 and the Fitbit Versa -- it's easy to find plenty of cheaper models, too. Our favorite cheap fitness tracker is the Fitbit Inspire HR, a no-frills tracker that is packed to the brim with sensors and still costs just $100. Even though it is cheap, the Inspire is backed by Fitbit, a brand that helped pioneer the fitness tracker market.

The Inspire HR is only one of several cheap fitness trackers we have on hand for testing. We've ran with them, slept with them, and worn them 24/7 for weeks to find out which ones are the best. We've compiled our favorites so that you're sure to find one to suit your needs -- and your budget. If you're looking to splurge, be sure to check out our compilation of the absolute best fitness trackers available.
The best overall: Fitbit Inspire HR

Read more
Before buying a Fitbit, check out these Garmin fitness trackers under $100
amazon garmin smartwatch deals forerunner

If you're looking for a great fitness tracker to keep tabs on your general health, then the Apple Watch and line of Fitbits are probably the best way to go. Not everyone, however, wants to spend a lot of cash on a fitness device -- and thankfully, for those people there are some great alternatives. If you're in the market for a Fitbit or smartwatch alternative on a budget, then check out these fitness trackers under $100. With budget options from Garmin and Amazfit, efficient activity tracking doesn't need to be overly expensive.
Garmin Forerunner 35 -- $100

Looking for a high-quality fitness tracker and don't mind hitting that $100 limit? The Garmin Forerunner 35 might be the smartwatch for you. The device looks much like any other smartwatch, plus it offers a GPD tracker, and a heart rate monitor that can monitor your heart rate 24/7. The device is great for more than just running, too -- it's got a 5 ATM water-resistance rating, meaning that it should be able to withstand depths of up to 50 meters. The Garmin Forerunner 35 is compatible with both Android and iOS smartphones, and can show notifications, control music, and more.

Read more