Campaign for better sleep: Fitbit's sleep metrics explained

Everything you need to know about Fitbit's sleep tracking
Fitbit's sleep metrics explained
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The more we learn about sleep’s impact on the body, the more we’ve come to understand how important it is. While there are still many mysteries surrounding sleep, we do know for a fact that it’s needed to repair and regenerate, mentally and physically, but it does so much more besides.


We spend a third of our lives sleeping so it pays to understand why good quality sleep is so important. That’s why sleep has been a central tenet of Fitbit’s health tracking ecosystem, and the company has worked with experts in the field from Stanford University, Johns Hopkins University and elsewhere to delve deeper into sleep and its importance on our wellbeing.

Today, any Fitbit device, whether it’s a brand new fitness tracker or smartwatch, can track and analyze your sleep, while Fitbit’s app can surface personalized tips and recommendations to help you sleep longer, better, stronger.

Check out how our team improved their slumber in our Campaign for Better Sleep:

Week 1: Does kicking caffeine and screen time improve your sleep?
Week 2: Why building sleep consistency is so important

How Fitbit tracks your sleep

Campaign for better sleep: Fitbit's sleep metrics explained

Fitbit’s been tracking sleep since the early days of the Fitbit Flex, but today its HR trackers can gleam so much more about our sleep habits. Heart rate data has played a big part in that, giving Fitbit new insights into not just the duration but the quality of our sleep.

At a basic level though, it comes down to movement. All Fitbit devices track movement with an accelerometer, and a long period of inactivity is indicative that you’ve drifted off. Fitbit combines your movement information with the heart rate sensor to track your vitals through the different stages of sleep.

At the end of the night, all this information is presented to you in the app, showing you how long you slept for, how well you slept and even how your heart rate changed through the night. Fitbit uses heart rate data from awake and asleep to estimate resting heart rate, and you’ll get better accuracy if you wear your device to sleep.

What are Sleep Stages?

Campaign for better sleep: Fitbit's sleep metrics explained

Sleep Stages are Fitbit’s way of examining the quality of your night’s sleep, using heart rate and accelerometer data to examine your vitals, as well as the movements you make during the night, which can help examine the quality of your sleep.


While you’re sleeping, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages.

When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night.

Sleep Stages is essentially concerned with the architecture of your sleep. Sleep can be analyzed in five different stages, however Fitbit actually simplifies this by grouping similar stages together. So in the app you’ll see Awake, Light, Deep and REM stages. But these aren’t portioned equally through the night.

During a sleep cycle, it’s most common to go from light sleep to deep sleep, back to light sleep, and then into REM sleep. Then the cycle generally repeats, but sleep patterns vary naturally.

Light sleep generally takes up 50-60% of your night’s sleep, while deep sleep and REM account for 10-25% each. When looking at your night’s sleep, Fitbit also compares your time spent in each sleep stage to others in your age and gender bracket using its Benchmark feature, so you can see how you shape up to the rest of the population.

Light sleep (which occurs within minutes of falling asleep) is essential for recovery and helps with memory in particular. Deep sleep – which will normally occur earlier in the night - is where your muscles repair and keeps your immune system healthy.

Finally, REM sleep is also important for memory and mental recovery, and as most of it tends to occur towards the end of the night. It’s associated with vivid dreams and can affect mood regulation, learning, and memory as your brain processes and consolidates information from the previous day so that it can be stored in your long-term memory.

Learning more with Sleep Insights

Campaign for better sleep: Fitbit's sleep metrics explained

Sleep Insights is where things get really smart. It’s here that Fitbit pulls together all your data - exercise, diet, weight - to see what might be affecting your quality of sleep. For example, if you fall asleep faster on nights where you’ve done evening exercise, Sleep Insights will connect those dots and suggest you keep your workout schedule to later in the day.


As with many things, repetition is the path to success, and the more you wear your Fitbit tracker the more you’ll benefit from Insights. Over time, this should help you better understand your body and the impact things like diet and exercise are having on your sleep. The more you use your Fitbit to track your sleep, the more Insights you’ll get and the more useful they’ll become.

Staying consistent with Sleep Schedules

Campaign for better sleep: Fitbit's sleep metrics explained

A really important factor for getting good sleep is consistency. That’s because our circadian rhythms work best when we have a consistent routine. Remember what we said about REM sleep coming mostly towards the end of the night? An inconsistent routine runs a higher risk of cutting that REM sleep short, leaving you feeling groggy throughout the day.

So the more you stick to the same bedtime the better you’ll find your sleep will be. Fitbit helps you manage this with Sleep Schedules, something you’ll find in the app. Here you’ll set a target sleep time and wake time for each day, and you should aim to do both within 30 minutes of your target.

Once set, you’ll get a notification on your Fitbit device and phone when it’s time to start winding down for bed. Fitbit devices also have a silent alarm feature that will use a vibration to gently wake you up at your set time.

Going further with Sleep Score

Campaign for better sleep: Fitbit's sleep metrics explained

Fitbit is taking things even further with the introduction of Sleep Score Beta, an experimental new feature currently in testing that is changing the way users can see their sleep information, while also delving into other areas like breathing patterns and blood oxygen levels.

Whereas Sleep Stages presents users with a graph of how they moved through different sleep levels during the night, Sleep Score Beta takes all this information and presents you with a number grade at the end of each night, which shows how good your sleep was. So if you woke up and saw a score of 85 you know you had a good sleep.

This number takes into account both the duration of sleep and the amount of time spent in each sleep stage, but it also looks at your respiratory patterns and - if you have a compatible Fitbit device - will monitor breathing disturbances and track your blood oxygen levels with the SpO2 sensor. This additional category of data is what Fitbit calls Revitalization and quantifies how restorative your sleep is.

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