Fitness watches and wearables have gone from niche gadgets for health tryhards to, basically, default gear for the everyday person. If you look around the gym or even the office, you’ll easily spot a WHOOP, Oura Ring, Garmin, or Apple Watch on someone’s wrist or finger. I’ve worn a couple of these over the years and currently am a WHOOP guy myself. They’re fun to use, and they hand you a pile of data that most people never had access to before: steps, HRV, sleep score, calorie burn, you name it. It’s all laid out in pretty graphs and tables, but most of the time, you have no clue what you are even looking at.

They’re also not cheap. For most people, these are a real financial decision, and the latest models just keep getting more advanced and expensive. As they become more common, you almost feel like you need to be sporting one of these bad boys to make sure you are doing this whole fitness thing right.

So this begs the question: Are these fitness wearables truly worth the hype, or are they just glorified accessories?

The Accuracy Problem

The biggest factor that can help answer this is the accuracy of these devices. The whole point of them is to track your fitness metrics, so we would hope these numbers are, at least, accurate. Right?

Well, luckily, researchers have conducted actual studies on this, so let’s see what the science says.

One of the best answers comes from a major scientific review in 2024, “Keeping Pace with Wearables,” that was published in Sports Medicine. A group of researchers reviewed nearly 400 studies on wearables, covering more than 430,000 people, and asked the exact question we are trying to answer: How accurate are the numbers?

Here’s a snapshot of what they found for some of the most common metrics fitness wearables measure:

Heart rate: This is one they tend to get right, usually coming within about 3% of the real number.

Step count: Tends to be slightly off, missing your real steps by around 10%.

Sleep: Gets overestimated. Your wearable usually thinks you slept longer than you actually did, and it can be way off on how long it took you to fall asleep.

VO2 max: Usually reads higher than it should, coming in about 15% off at rest and 10% during exercise testing.

Workout intensity: One of the least accurate things researchers measured, with readings off by anywhere from 29% to 80%.

Calories burned: This was the worst of them all. More on this in the next section.

To be fair, the researchers did note that there is so much variation among brands and devices that there really can’t be a blanket accuracy baseline applied to all of them. However, one number that really jumped out to me was that only about 1 in 10 fitness trackers was actually tested and proven accurate for even one of the biometric claims measured, meaning most of what’s strapped to people’s wrists has never really been checked for the validity of its measurements.

Calorie Burn: The Worst Offender

If that wasn’t bad enough, the one number that everyone looks at the most is the one you need to trust the least: total calories burned.

A 2020 meta-analysis in the British Journal of Sports Medicine, entitled “How Well Do Activity Monitors Estimate Energy Expenditure?,” looked at 60 different studies comparing watch-reported calorie burn with the real thing. What researchers found was that calorie measurements were all over the place. Some watches were way off, some less so, and the accuracy changed depending on the workout.

A newer study published in Physiological Measurement, “Apple Watch Accuracy in Monitoring Health Metrics,” zoomed in on the Apple Watch, since it comes from one of the more trusted brands. Researchers analyzed 56 studies and found that the Apple Watch was off by almost 28% when it came to calories burned. 

This isn’t just an Apple problem. Another study, “Accuracy and Acceptability of Wrist-Wearable Activity-Tracking Devices,” in the Journal of Medical Internet Research, looked at 65 research papers and found every brand tested was off by more than 30% on calories burned. Not one brand got it right.

To illustrate this, let’s say your watch tells you that you burned 600 calories during a workout. With that kind of error, the real number could be 200 calories, or more off in either direction.

Put plainly, these devices aren’t as precise as most people assume because figuring out someone’s true energy expenditure during a workout is genuinely hard. That kind of calculation normally takes clinical equipment to determine, not just a sensor that lives on your wrist all day.

Why the Inaccuracies May Not Be Such a Big Deal

Now, I know the bulk of this article is talking smack on these wearables, but I promise there is a happy resolution, especially since I still wear one.

Here’s the part that took me a while to land on: Despite the inaccuracies, these gadgets can still be very useful. You’re only using them wrong if you’re treating them as precision instruments.

What we need to understand is that these were never the best data tools to begin with. However, they can be some of the best behavior tools to spark real change. The number itself isn’t the point. The biggest takeaway is whether seeing that number changes what you actually do.

If your fitness wearable shows you that your daily activity is the same as being comatose and that gets you up to go for a walk, then it did its job. If your sleep score bothers you enough that you finally start going to bed on time, then it worked. If seeing the calories burned pushes you to get that last extra rep or spend a couple more minutes on the treadmill, then that’s a win in my book.

The majority of people don’t have a “needing the right numbers” problem. They have a “not having enough good habits to begin with” problem. The first step to any lifestyle change is awareness of your current behaviors, and these wearables do a great job of that. But there is one important principle you need to understand to truly get the most out of them.

Trust the Trend, Not the Number

If there’s one thing you can take from this article that is worth remembering about these devices, it’s this:

Stop caring about the exact number and start watching the direction of the trend.

These devices aren’t always great at providing accurate individual measurements, but they can still be useful for showing how those measurements change over time. Say your watch spits out that you burned 400 calories in one workout and 550 in the next. Is either number exactly right? Probably not, but it’s a fair bet that you worked harder in the second one.

So if you were trying to push it in the gym, you should probably shoot for a “calorie burn” close to 550. Not because you actually burned that many calories, but because you likely matched the effort of that workout.

This goes for the other metrics as well. If you want to improve a certain number, make sure the overall trend of the data is going in the right direction, instead of focusing on the absolute number itself. It’s not perfect science. It’s how you can actually use these devices in a way that gets you closer to your goals, instead of being bogged down by the numbers they provide.

So, Is It Worth It, or Not?

Before you drop some serious cash on one of these, you should ask yourself three questions:

What metric am I actually looking at, why am I tracking it, and what am I going to do differently because of it?

If your answers drive real change and lead you to form new habits that benefit you, then yeah, it’s honestly a solid investment. If you’re just watching numbers move around on a screen but still living the exact same way you did before getting one, then you’re better off saving your money.

These gadgets are cool tools, but they’re not required to achieve your fitness goals. Use them to build awareness and drive better behaviors, and they’ll earn their price tag, for sure. But if nothing changes or you don’t know why you’re tracking these numbers to begin with, then it’s just a pricey distraction that happens to come in different colors.