Fitbit Estimated Oxygen Variation: We explain SpO2, sleep apnea and blood oxygen

We speak to Fitbit scientist about how it all works
Fitbit Lifestyle photo of Fitbit Versa 2.,,Photographer: Matt Hawthorne.
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One of the most important metrics on a Fitbit tracker is the Estimated Oxygen Variation – and now that every tracker is fitted with an SpO2 sensor, everyone can take advantage.

Blood oxygen can be used to detect sleep conditions such as sleep apnea, and offer a better analysis of what's going on with our bodies in those lost hours.

But Fitbit's Estimated Oxygen Variation data needs a little explanation.

We spoke to Dr. Conor Heneghan, Fitbit’s Lead Sleep Research Scientist to explain everything you need to know.

What is Estimated Oxygen Variation?

Estimated Oxygen Variation is a reading of the oxygen levels in your blood. This is done via the SpO2 sensor, which is a red LED in the optical heart rate monitor.

Your Fitbit tracker will track blood oxygen saturation as a percentage, which you can see in your Health Metrics dashboard. But Estimated Oxygen Variation is different.

Fitbit's detection is a little different. This metric examines the difference in the highs and lows of your blood oxygen levels and looks to highlight potential underlying conditions.

It's important to note that  Estimated Oxygen Variation is a Fitbit Premium feature, so on;y subscribers will see it.

Fitbit devices with Estimated Oxygen Variation

FitbitFitbit family

The feature can be found on any Fitbit tracker with a SpO2 sensor. And with the launch of the Inspire 3, that means all of the current range is eligible.

This includes:

  • Fitbit Versa 4 (and all Versa models)
  • Fitbit Sense and Sense 2
  • Fitbit Charge 3/4/5
  • Fitbit Luxe
  • Fitbit Inspire 3

Estimated Oxygen Variation Graph explained


You'll find Estimated Oxygen Variation in your sleep stats. Head to sleep stats, choose a night's sleep, and go to the Restoration tab.

Unlike some devices that will give you a number for your blood oxygen level. However, a Fitbit spokesperson told us that the graph provided by Fitbit is an "estimation of the variability of oxygen levels in the bloodstream".

It's not a graph of the actual SpO2 estimate.

The example screenshot above shows what the graph will look like – and from what we can see, blood oxygen is monitored by the sensor during sleep – and variations that could show a sleep apnea issue are highlighted on the graph.

Essential reading: Fitbit's Sleep Score explained

"We're showing a metric that correlates with the average variability of your blood oxygen level," said Dr. Conor Heneghan.

"Let’s say Person A has oxygen level of 96% +/-1% and Person B has oxygen level of 95% +/- 4% throughout the night, then Person B will see a higher “estimated oxygen variation” throughout the night. We calculate this every minute."

Can Fitbit track sleep apnea?

Wareablefitbit oxygen data

"We are not claiming this can be used to correlate with sleep apnea status," said said Dr. Conor Heneghan. "No, there is not currently an alert within the device or app. This graph is another opportunity for us to provide more data to our users."

So while a large level of variation in blood oxygen COULD show sleep apnea – Fitbit won't spell this out for you. But you might want to get it checked out.

"Seeing frequent big variations is a clue that you may be experiencing breathing disturbances during sleep—something you might want to talk to your doctor about, particularly if you experience symptoms such as excessive tiredness, loud snoring, or gasping during sleep. Keep in mind that how you wear your device can also affect this data."

There are lots of caveats here, not least the "estimated" part of the Fitbit name. It's likely the company got fed up waiting for FDA clearance in the wake of competitors getting similar features out onto the wrists of consumers. So, for now, you need to check the data and make your own conclusions.

What else can Estimated Oxygen Variation Graph show?

Of course, blood oxygen isn't all about sleep apnea.

"Sleep apnea is a common cause of variation in oxygen level, but sleeping at altitude can also increase variability. It’s probable that some types of heart failure are associated with variation in oxygen level, too (Cheyne-Stokes respiration)," said Dr. Conor Heneghan.

So while Fitbit isn't claiming this to be a medical feature, if you're seeing high instances of Estimate Oxygen Variation, you might want to show that data to your doctor.

How we test

James Stables


James is the co-founder of Wareable, and he has been a technology journalist for 15 years.

He started his career at Future Publishing, James became the features editor of T3 Magazine and and was a regular contributor to TechRadar – before leaving Future Publishing to found Wareable in 2014.

James has been at the helm of Wareable since 2014 and has become one of the leading experts in wearable technologies globally. He has reviewed, tested, and covered pretty much every wearable on the market, and is passionate about the evolving industry, and wearables helping people achieve healthier and happier lives.

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