Your Fitness Tracker Comes With Lots of Sleep Data. Here’s How to Make It Work for You.

When you first get a fitness tracker, it’s tempting to start diving into the daily data from your new toy ASAP—and maybe even obsessing over it. But if you really want to make lasting improvements to your routines, it’s better to look at your sleep-number averages over a longer period of time, at least a month, according to Chris Winter, MD, a neurologist, sleep specialist, and host of the Sleep Unplugged podcast. That’s because a single night of sleep, no matter how good or bad, can prove to be an outlier and has no bearing on your actual long-term health or sleep habits.

“If you were awake for 20 minutes at 3 a.m. last night, that alone doesn’t make you a terrible sleeper,” Winter said in a phone interview. “You need to focus on your long-term patterns instead.”

Taking a broader view of your sleep data is especially helpful since trackers and apps can occasionally generate inaccurate data points, Winter said, but “have proven to be pretty accurate when viewed on a long-term basis.”

Many fitness trackers and sleep apps offer a “score” for your nightly sleep, usually on a scale of 1 to 100. Getting an easy-to-understand grade may delight you on the mornings you wake up to a high score—and then fill you with self-loathing whenever your score takes a nosedive. Either way, though, the experts we spoke to said not to put much stock in your scores, whatever they may be.

“Sleep scores will often be based on sleep duration and regularity, probably with a little bit of your nightly wakefulness mixed in. But the algorithms that translate all this into a score are very proprietary, so you’ll never truly know what your sleep score is based on,” Seema Khosla, MD, the medical director at North Dakota Center for Sleep, said in a phone interview. Moreover, trackers and apps may frequently update and upgrade those algorithms, she added, “so even if you feel you’ve got a handle on what your sleep score means, the next iteration will probably be a little bit different.”

“When you're trying to figure out how well you slept last night, first decide how you feel when you wake up—then look at your tracker,” Khosla said. “One thing I tell my patients is, ‘I want to know how you felt rather than what your Fitbit told you about how you slept.’”

In fact, if you are already satisfied with your sleep, collecting nightly data might just muck up a good thing. “If you wake up feeling refreshed and don’t find that you want to sleep during the day, but your tracker shows multiple awakenings at night, then that data might not be actionable,” Khosla said. “We don’t want to treat the score. We want to treat the patient and their specific sleep problem, but only if it’s a problem.”

Although how a person feels after a night’s sleep can be very telling, “we often misperceive what happens during sleep,” Winter said. “In those cases, objective data can be very transformative.”

For example, Winter and Khosla both told us that people who snore—a habit that can indicate sleep apnea—sometimes don’t believe that they snore, even if the person they share a bed with has repeatedly told them that they do. Because many fitness trackers can track blood oxygen saturation (often abbreviated as SpO2; lower levels of saturation can be a sign of snoring), your device might make the case in a more credible way and thus convince you that your snoring is something that you and your doctor need to check out further.

“When the idea is abstract, a patient might say, ‘You’re trying to sell me a CPAP. I don’t buy it.’ When you show patients that their oxygen saturation went down to 70%, all of a sudden it’s, ‘Holy smokes,’” Khosla said. “It’s very real.”

The same advice can apply to those who tend to describe their sleep in unrealistic ways, such as with statements like “I spend half the night lying awake” or “It takes me forever to fall asleep.”

Chances are, you are not taking “forever” to fall asleep, nor are you likely spending half the night lying awake. While you might be assuming that you’re a terrible sleeper, your tracker may show you that your wakefulness doesn’t last as long as you think it does, and that you’re actually getting a good amount of sleep overall. This, in turn, can make you less anxious about your sleep.

“The best, most grabbable data point that these devices provide is the overall amount of sleep,” Winter said. “That’s the thing that most people can do the most with, because most people understand that we should all be getting around seven to eight hours of sleep a night.”

As for sleep quality, such as how much deep sleep or REM sleep you’re getting, “take that with more of a grain of salt,” Winter said. “Those data points are a little more fraught with inaccuracies and also a little more abstract, which could leave you feeling like, ‘I don’t know what to do with this.’” (In an interview for our guide to the best fitness trackers, Aric A. Prather, a professor of psychiatry at the University of California San Francisco Weill Institute for Neurosciences, agreed that the majority of these devices can accurately measure total sleep time, but “this is less true when it comes to sleep architecture, like minutes in deep sleep.”)

How is your sleep affected if you decide to down an extra cup of coffee at 4 p.m.? Can you get away with a couple of glasses of wine after dinner without ruining that night’s sleep? And does it matter how late you eat that dinner?

After your tracker has helped you establish what a good night’s sleep looks like, numerically speaking, it can be a great tool for determining or reaffirming how certain lifestyle choices might do a number on your slumber.

“The big ones are exercise, food, and caffeine—but surprisingly, the biggest one is probably your bed partner,” Khosla said. “You may learn that you sleep a lot better when your spouse or pet isn’t in the bed or bedroom with you.” (If that’s true for you, but you’re not looking to get “sleep divorced” just yet, our New York Times colleagues have some advice.)

Khosla also suggested using your newfound data to reinforce healthier habits. “In medicine, perfection is the enemy of the good,” Khosla said. “If you find out that alcohol affects your sleep, that doesn’t mean you never have to drink again. But maybe you’ll choose to have those drinks earlier in the night, or have two drinks instead of three.”

For some fitness tracker wearers, striving for a perfect sleep score or fixating on daily data points can lead to sleep anxiety. In fact, the phenomenon is common enough that, in 2017, an article in the Journal of Clinical Sleep Medicine coined a clinical term for it: orthosomnia. The article’s authors likened it to the similarly unhealthy preoccupation with healthy eating known as orthorexia.

“Sleep anxiety can be really scary. I’ve seen patients come in and tell me, ‘Look at this data; my sleep is awful. Am I going to die, am I going to get Alzheimer’s?’” Khosla said. The data that patients anguish over, however, is rarely as concerning as their beliefs that they’re terrible sleepers, “especially since poor sleep kind of begets poor sleep,” she added.

If you find that your tracker exacerbates certain insomnia symptoms—which, according to the Mayo Clinic, include “[h]aving ongoing worries about sleep”—the solution may simply be to turn off or remove your tracker at night, at least until your anxiety subsides. “We put a lot of pressure on ourselves to do a lot of things right,” Khosla said. “Being kind to ourselves is actually a great way to help us get better sleep.”

This article was edited by Alexander Aciman and Catherine Kast.