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I wore an Apple Watch and a Fitbit to track my sleep. Here's how the data compared
Fitbit has been cornering the fitness and sleep tracking market for years, but Apple upped its game recently with WatchOS 9. If you're trying to decide which type to buy, here's how these wearables do with sleep tracking.
There's a common ailment that plagues me and many others around the world: I stay up too late and then wake up exhausted, and drag my feet all day, only to repeat the cycle again each night. Most of us know we're supposed to get the ideal 7 to 9 hours of sleep every night, but are you actually getting them? I sure as heck am not.
So I decided to get a sleep tracking device. I love data and seeing things in black and white, so when it was brought to my attention that maybe some of my stress was rooted in lack of sleep, I thought a sleep tracker might help.
My research turned up great things about Fitbit's sleep tracking algorithm, so I bought a Fitbit Inspire 2 as the first step to mending my broken sleep. And I'm not the only one to take this step: According to the Journal of Clinical Sleep Medicine, 10% of adults in the United States wear or use a sleep tracking device on a regular basis.
Why I wear both a Fitbit and an Apple Watch
The Fitbit showed me that I was getting even less sleep than I thought I was. I'd expected to see a lot of wake-ups that I'd be able to attribute to tending to my 1-year-old, but, worse than that, I found that I was averaging about 4.5 hours of sleep at night, some nights just barely making it past 3 hours.
The perfectionist in me quickly accepted the challenge and I became enthralled by sleep data; I would wake up every morning eager to see my stats and began making conscious decisions looking to get not just more sleep, but better-quality sleep, all with the purpose of improving my score.
Around this time, I also got an Apple Watch 7, but found I couldn't part with my Fitbit. After it said the giraffe is my sleep animal, my Inspire 2 and I were buddies. Plus, Apple hadn't released WatchOS 9 yet, so there was no native tracking feature that could show me my sleep cycles and stages like my precious Fitbit could.
That changed with the release of WatchOS 9 in September 2022, which enables compatible Apple Watches to track sleep stages and cycles. My watch leveled up in the sleep tracking department to better compete with my Fitbit.
Does the Apple Watch track sleep better than a Fitbit?
The jury is still out. Since the new WatchOS that tracks sleep stages and cycles has only been in widespread use for a few months, there's no definitive answer on the accuracy of its sleep tracking yet. Until some peer-reviewed studies comparing it with other tried-and-true methods are published, anecdotal evidence is all we've got.
I'd love to do an actual sleep study while wearing my Apple Watch and Fitbit to see how accurate they are at determining sleep stages -- that's how much I love tracking my sleep. For now, I can only see the data from having worn both devices to bed for months.
Though I don't know which one is more accurate, I've found the Apple Watch 7 consistently does three main things differently from the Fitbit Inspire 2. The data below is a daily average over seven days of sleep tracking, where both devices tracked sleep cycles on the same nights.
1. The Apple Watch shows more light or core sleep and less deep sleep than the Fitbit
Fitbit Inspire 2
Apple Watch 7
4 hr, 51 m
5 hr, 16 m
1 hr, 3 m
2 hr, 23 m
3 hr, 24 m
1 hr, 9 m
1 hr, 38 m
Tracking your sleep stages and cycles is most accurately done by polysomnography; it's not as simple as monitoring your heart rate all night. Polysomnography analyzes your sleep by tracking your brain waves, breathing and heart rate, blood oxygen level, and eye and body movements throughout the night. While you sleep during a polysomnogram, an electroencephalogram (EEG) can be performed to measure your brain waves, aka the electrical activity in your brain as you navigate different sleep stages.
All these fancy words basically mean that, at this point in modern technology, you can't track sleep cycles with 100% accuracy with devices you wear on your wrist, but you can make approximations with a combination of different data sources and a great algorithm or two. This is what wearables do.
As you can see on the table above, my Apple Watch tends to track longer time asleep than the Fitbit by about 25 minutes on average, while also tracking slightly more time awake throughout the night. However, the biggest differences are in Light/Core sleep and REM sleep; the former is marked as over an hour longer by my Apple Watch 7, while the REM sleep is about 40 minutes longer.
2. Asleep and awake times are pretty even for both, with less than a 20-minute difference
Fitbit Inspire 2
Apple Watch 7
Awake for the day
While my Fitbit showed less time asleep than the Apple Watch did, by an average of 25 minutes, the data I've seen over the past couple of months makes comparisons between both devices a toss-up: Some days my Fitbit says I fell asleep several minutes or up to an hour before the Apple Watch marked the onset of sleep, times when I was lying in bed reading my Kindle or, yes, watching TikTok.
On other days the Apple Watch marks sleep onset earlier than my Fitbit, resulting in times like the ones shown above. Many factors can make this more or less accurate, like how tight or loose your device is, which wrist you wear it on, and how much you move at night.
3. Shows "Time asleep" as longer than "Time in bed" about half the time
The new update to the Apple WatchOS gives it the ability to track sleep stages by analyzing heart rate and movement, and it does so with at least some accuracy: though it's still too soon for published, peer-reviewed studies, my anecdotal impression is that the Apple Watch is more accurate than Fitbit at sleep tracking.
Some other anecdotal examples, like scientist's Rob ter Horst's sleep tests (video), also found the Apple Watch post-WatchOS 9 update to be the most accurate at tracking sleep cycles of the devices he's tested.
But one thing that grinds my gears is that the Apple Watch tends to show my total time asleep as longer than the total time I actually spent in my bed, as shown in the picture above. Complaints from other users show this isn't a new problem, and it makes me question the accuracy of the sleep tracking data the Apple Watch gives me.
You should buy an Apple Watch if...
You're an Apple person who wants a smartwatch with solid sleep tracking.
The Apple Watch has more features than a fitness tracker, like more third-party apps, for example, and fits seamlessly into the Apple ecosystem.
As far as sleep tracking, anecdotal evidence is split so far, but I've preferred tracking with my Apple Watch 7 since the WatchOS 9 features rolled out. I find that it's more often accurate on showing my sleep onset time and the times I wake up during the night, but I can't speak for the sleep stages data without further evidence.