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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 just upped its game with the new WatchOS 9. If you're trying to decide which one to buy, here's how they do with sleep tracking.
Written by Maria Diaz, Staff Writer on
Fitbit Inspire 2 and Apple Watch 7 side by side on a blanket

My Fitbit Inspire 2 and Apple Watch 7 compete each morning to provide the most accurate sleep data.

Maria Diaz / ZDNET

There's a common ailment that plagues me and many others around the world: I stay up too late and wake up exhausted, only to drag my feet all day and repeat the cycle each night. Most of us know we're supposed to get the ideal 7-9 hours of sleep every night, but are you actually getting them? I sure as heck am not.

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So I decided to get a sleep tracking device. I love data and seeing things in black and white, and when it was brought to my attention that maybe some of my stress was rooted in lack of sleep, I thought a sleep tracker may 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; 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. 

Also: Black Friday smartwatch deals: Get an Apple Watch for $179 right now

Why I wear both a Fitbit and an Apple Watch

Hand holding a Fitbit Inspire 2 and Apple Watch 7 side by side

Even after getting an Apple Watch, I wasn't able to part with my Fitbit.

Maria Diaz / ZDNET

The Fitbit showed me that I was getting even less sleep than I thought I was. I'd originally thought I'd see a lot of wake-ups that I'd be able to attribute to my one-year-old but, beyond that, I found that I was averaging about 4.5 hours of sleep at night, some nights just barely making it past three hours. 

The perfectionist in me was unleashed and I became enthralled by sleep data; I would wake up every morning eager to see my stats and began making conscious decisions to get, not just more sleep, but better quality sleep, all to improve my score. 

Around this time, I also got an Apple Watch 7, and found I couldn't part with my Fitbit. After it said the giraffe is my sleep animal, my Inspire 2 and I are buddies now. Plus, Apple hadn't released WatchOS 9 yet, so there was no native tracker that could show me my sleep cycles and stages like my precious Fitbit could.

That is, until the release of WatchOS 9 in September 2022, which enables compatible Apple Watches to track sleep stages and cycles.

Does the Apple Watch track sleep better than a Fitbit?

The verdict is still out. Since the new WatchOS that tracks sleep stages and cycles is still only a couple months old in widespread use, there's no definitive answer on the accuracy of its sleep tracking. Until some peer-reviewed studies comparing it with other tried-and-true methods are published, anecdotal evidence is all we've got.

Also: How to sleep better with the Apple Watch

Personally, I've found the Apple Watch consistently does three main things differently from the Fitbit; whether one is more accurate than the other is yet to be known. I must note that, while I've worn both devices to bed for months, this data below is only a daily average of seven days' worth 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. 

MetricFitbit Inspire 2Apple Watch 7
Time asleep4 hr 51 m5 hr 16 m
Time awake48 min1 hr 3 m
Light sleep2 hr 23 m3 hr 24 m
Deep sleep1 hr 9 m48 m
REM sleep58 m1 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, or EEG, can be performed to measure your brain waves, aka the electrical activity in your brain as you navigate different sleep stages.

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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 have at home, 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. 

I'd love to do a sleep study while wearing my Apple Watch and Fitbit to see how these square up in accuracy of determining sleep stages, but for now, I can only see the data in front of me. 

2. Asleep and awake times are pretty even for both, with less than 20-minutes difference.

MetricFitbit Inspire 2Apple Watch 7
Sleep onset1:40 AM1:18 AM
Awake for the day6:45 AM6:53 AM

While my Fitbit determined 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 sleep onset, when I was laying in bed reading my Kindle or, yes, watching TikTok.

Also: How to get (great) free books on Kindle

Obviously, it evens itself out with other days, where the Apple Watch marks sleep onset earlier than my Fitbit, resulting in the times 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, among many others.

3. Shows "Time asleep" as longer than "Time in bed" about half the time.

Screenshot of Apple Watch sleep data

Six of the seven instances where my Apple Watch has recorded longer times asleep than times in bed in the past 30 days.

Maria Diaz / ZDNET

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 is still to soon for published peer-reviewed Apple Watch sleep tracking studies, my anecdotal evidence is that the Apple Watch is more accurate than Fitbit to track my sleep, for now.

My Fitbit has overestimated my time asleep a lot in the past, inaccurately marking me "asleep" when I'm just laying down reading, for example. Some other anecdotal examples, like scientist's Rob ter Horst's sleep tests, also found the Apple Watch to be the most accurate of the devices he's tested at tracking sleep cycles post-WatchOS 9 update.

Also: Apple Watch Ultra vs. Garmin Enduro 2

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. Complaints from other users means this isn't a new problem, but it is one that makes me question the accuracy of the data the Apple Watch gives me for my sleep tracking.

You should buy an Apple Watch if...

Apple Watch 7 on blanket

Apple Watch 7 with data from a night's sleep on display.

Maria Diaz / ZDNET

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 a seamless fit into the Apple ecosystem.

Some features are exclusive to the Apple Watch Series 8, like crash detection, which can alert emergency services in the event of a car accident, for example, and temperature tracking, which could help women track ovulation through changes in basal body temperature.

Also: Apple Watch Series 8 vs Apple Watch Series 7

As far as sleep tracking, anecdotal evidence is split, but I prefer tracking with my Apple Watch 7 since the WatchOS 9 features rolled out. I find that it's most 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. 

You should buy a Fitbit if...

Hand holding a Fitbit Inspire 2

The tiny and adorable Fitbit Inspire 2

Maria Diaz | ZDNET

You're team Android, and/or looking for a top-of-the-line fitness tracker with sleep tracking. 

Because Fitbit can sync with both iOS and Android, it's also a better option for Android users, since the Apple Watch is exclusive to iPhone owners. 

Also: The best Fitbits 

The lineup of Fitbits is also much more affordable than the Apple Watch, so if you're on the market for a fitness tracker but don't want to spend too much, this is likely a better choice. 

Though they don't have as many features as the Apple Watch, Fitbit also has a line of smartwatches, like the Fitbit Sense 2, Fitbit Versa 4, and Fitbit Versa 2, as well as Fitbit tracking on the Google Pixel Watch.

Review: Fitbit's Sense 2 gave me a glimpse of how the Google Pixel Watch will be

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