Fitbit’s Sleep Score: New metric and the SpO2 sensor explained

Putting Fitbit's big new sleep feature to the test
Living with Fitbit Sleep Score
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Sleep science is where Fitbit has managed to outpace its rivals, and it’s become even more useful with the introduction of Sleep Score.

If you've opened up the recently revamped Fitbit app, you might have noticed the Sleep Score feature has finally come out of beta and is available to all. The feature offers a new way to review and interpret the sleep data tracked from a Fitbit device.

Fitbit Sleep Score SPO2
The new Sleep Score interface

Sleep Scores are available if your Fitbit is equipped with a relative SpO2 sensor, which to date includes the Charge 3, Versa, Versa Lite, Ionic and recently announced Versa 2.

But, we should clarify that the current version of Sleep Score now available does not use that sensor to generate the score. It did in our experience with the beta version, but once it's ready to be put to use for all, insights into breathing quality and blood oxygen levels will be factored into your overall Sleep Score.

Amazon: Fitbit Versa 2
Amazon: Fitbit Versa 2

Now that Sleep Score is out of beta, it's been revealed that certain elements are exclusive to Fitbit Premium members. Namely, if you want to see your Sleeping Heart Rate, and to have access to programs designed to improve your sleep, you'll need to subscribe to the new service.

Essential reading: Why Fitbit and Apple want to conquer sleep apnea

We tested out Sleep Score while it was still in beta by wearing a Fitbit Charge 3 for a week. You can read about our initial experience below, along with more information on just how your Sleep Score is calculated.

New sleep numbers

Fitbit Sleep Score SPO2

The most immediate change is the introduction of a Sleep Score at the end of each night.

“Some feedback we got was to simplify it into a single number so people could come have a simple metric,” said Dr Conor Heneghan, lead sleep research scientist at Fitbit.

So any score above 80 would be considered a good night’s sleep, something in the 70s would be fair, and anything below that is… not great. Fitbit says that most users get a score between 72 to 83.

But this number is made by combining three other scores, which Fitbit also breaks out. The first is Sleep Duration, which looks at your length of sleep and compares to your average bedtimes and wake-up goals.

It also compares your sleep duration against the average score for your age/gender bracket. Sleep Depth, the second score, is calculated from how much time you spend in deep sleep and REM within your benchmarks.

The third score, Restoration (referred to as Revitalization during the beta), is a little more interesting. Here Fitbit is using data from the SpO2 sensor to measure your blood oxygen saturation during sleep. It also looks for breathing disturbances and compares your heart rate during sleep to wake hours.

Even though my sleep duration was good on both those nights, travel had a visible impact on my Revitalization score

This will be the first time Fitbit’s relative SpO2 sensor has a visible use, but there are many other factors wrapped into the Restoration score.

For example, if your heart rate is elevated during sleep due to stress or oncoming illness, your Restoration index will be lowered.

I tested Sleep Score over a week in which I’d be travelling a lot. A 15-hour plane journey would certainly affect both my sleep patterns and my oxygen saturation.

Pulse oximetry tests have shown that high-altitude travel has an effect on oxygen saturation, so I knew that even on a plane like the Boeing 787, which locks its cabin air pressure to 6,000 feet altitude (most other planes keep it between 6,000 and 8,000), would still be enough to knock my oxygen levels down a bit.

Fitbit Sleep Score SPO2

And sure enough, it did. See how my Revitalization (now Restoration) dropped to between 45-50 between on Friday and Sunday. Even though my sleep duration was good on both those nights and my sleep depth wasn’t terrible, travel had a visible impact on my score.


Going deeper

Fitbit Sleep Score SPO2

It’s in the Restoration index that Fitbit says it will look for signs of asthma, allergies and even sleep apnea. Sleep apnea, where breathing stops and starts during sleep, causes blood oxygen levels to fluctuate.

If your Fitbit sees your oxygen levels are low during sleep, and that your sleep is often disturbed, it will let you know that something is wrong, and that you should maybe see a doctor.

Read this: Everything you need to know about your Fitbit

But until Fitbit gets FDA clearance, it won’t actually be able to say that these patterns are indicative of asthma, sleep apnea or other conditions.

Instead you’ll get a notification telling you that there is variation in your sleep quality that seems to be related to breathing, and Fitbit will highlight some things that could be affecting this.

“We’re continuing our clinical trials to collect the data to support that final application,” said Conor, discussing the company's work with the FDA. “We’re still at the early stages of testing.”

Fitbit users with devices that don’t have an SpO2 sensor will still get the new Sleep Score features, but won’t get any specific information about breathing quality.

Fitbit Sleep Score SPO2

As part of the beta trail, Fitbit is giving participants a survey each morning asking how well they slept, how much energy they have and whether they drank coffee, alcohol, or worked out close to bedtime.

Users won’t get these questions when the feature finally rolls out, but right now it’s helping Fitbit improve the system. Heneghan said that Fitbit will run the trial for two to three months, giving it time to tweak the algorithms and how the factors are weighted.

Read this: The best cheap Fitbit deals

So the big question is: does any of this make Fitbit’s sleep tracking better? I think for a lot of people, simplifying all this information into a nice round score will certainly help.

Currently Fitbit displays the night’s sleep as a graph of sleep stages with another to show how your results compare to your demographic. But this may be needlessly complicated for people who are getting the right amount – and quality – of sleep, while those who aren’t have the option to dive deeper into the data.

More interesting is that this marks another step forward in Fitbit's quest to be more diagnostic, and with Apple’s ECG now live in the Apple Watch, the race is most definitely on.

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  • CarolineR·

    I am interested in a watch that accurately measures SpO2. For me it is not a game it is because I need it for health reasons. I need to exercise, but I must monitor it and not pretend which is what so many have said about their purchase. Is there a good one with accurate SpO2?

  • Yooper·

    Does this in fact use the SPO2 sensor as mentioned? I ask because I have the Versa and looked into the details within the app of how it's calc'd and it only mentions comparing resting and sleeping heart rate (for Restoration), no mention of use of the oxygen sensor. Has this been confirmed? Thanks.

    • m.sawh·


      The version of Sleep Score currently available does not use the SpO2 sensor. Our piece was based on the beta version of the feature, which did offer us the ability to see that data. Hopefully it will be included soon, but as yet, Fitbit has not confirmed when that will be. We've clarified this in the article as well.

  • Whateveryo·

    I am writing to tell you about my disappointment in the new Fitbit Sleep Score you wrote about recently. Not only is the feature not optional, it actually replaces the previous feature of calculating your average sleep for the week. On closer inspection, one discovers that Fitbit has presently removed this feature in anticipation of charging money for it in the future.

    If Fitbit had truly been most concerned about the ease of interpreting sleep information, the obvious choice would have been to allow users to choose between a "Sleep Score" view and an "average hours" view. But what likely really happened is more sinister, and ill-advised to boot. This type of greed is transparent and unacceptable to consumers. Brands that remove previously free features in order to upsell a premium option often lose loyal customers. Perhaps Fitbit would not be pushing this new anti-consumer strategy if they believed that consumers would lash back.

    I'm not sure if you've received similar feedback about this issue, but if you are interested in writing an article about it, you may find that many Fitbit customers are willing to offer up their negative experiences with the new update, myself included.

  • Vegemate·

    I upgraded the app which includes sleep scores a few weeks ago. To start with I thought it was ok, until it started telling me that my sleep was "poor" or "fair". This fostered a feeling of "failing" at sleeping. I bought the Fitbit purely because of its credentials on sleep monitoring because of issues with sleep. I tried to find a way to get rid of the "sleep store" because it was causing me anxiety and discovered that it can't be done. On recently seeing my doctor and my mental health care professional in the last week, they both suggested that I stop using the app, advice which I have taken. I now agree with the advice I was given, that summing up the quality of a persons sleep with a single number is ridiculous as there are too many variables, and the information can only be properly be interpreted by a person with the appropriate professional qualifications.

    What Fitbit are trying to do here is admirable however, as far as I'm concerned they haven't got this one right and should at the very least make the sleep score a opt-in option.

  • Ft386·

    Regular and long-time FitBit users hate - and I mean really really hate - the Sleep Score. The primary complaint is that by giving users something more simple, FitBit has taken away the ability to see weekly average hours slept, week by week. The Score feels judgmental and confusing and I think that’s what FitBit is literally banking on. If you want to see the Sleep Score details, you have to purchase their premium subscription.

    Can you imagine if FitBit started handing out scores on calories burned or consumed? People don’t want FitBit to tell them what their data means. They just want the data so they can judge for themselves how it fits into their lives.

    Check out the FitBit community and the Feature suggestion forum. People are livid about the change. I’ve never seen anything like it. FitBit truly screwed up with this change