How Does Fitbit Track Sleep? Understanding the Sleep Stages Feature

Learn how to track your sleep using your Fitbit

You'll find several devices for tracking sleep on the market. Among them are fitness trackers, including many Fitbit models. Sleep Stages, a Fitbit feature, is designed to help you get your best sleep.

Many Fitbit trackers tell you how long you are asleep and the type of sleep you get while under the sheets. Curious how it works? Here's a rundown on the feature and an explanation of the different sleep stages your Fitbit tracks.

Fitbit Charge 2 Activity and Sleep Tracker

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Which Device Do I Need?

To take advantage of the Fitbit Sleep Stages technology, you need to use a device that supports it and can monitor your heart rate. Most newer Fitbits, such as the Fitbit Charge 5, Fitbit Luxe, and Inspire 2, can track sleep, and some of the older ones can as well, such as the Fitbit Alta HR, Fitbit Blaze, and Fitbit Charge HR.

These are all wrist-worn trackers, and you need to keep them on for the entire night for the feature to work.

How Does Fitbit Know I'm Sleeping?

If you went to a doctor for a sleep study, your sleep stages would be measured by an electroencephalogram that pays attention to your brain activity. You'd also be hooked up to other machines that monitor your muscle movements.

While your Fitbit is not a replacement for going to see a sleep specialist, it detects some of the same things by monitoring your heart rate and your movements while you're sleeping or attempting to sleep. Using those measurements, it makes reasonable guesses. For example, if your heart rate remains about the same and you don't move for an hour, the chances are good you're asleep.

Fitbit Charge 2 Heart Rate & Fitness Wristband


Fitbit monitors your heart rate variability (HRV) while you sleep, which helps it determine when you're moving between levels of sleep. The ratings aren't going to be as robust as those you get from a doctor, but if you're looking for some basic information about yourself and your sleep patterns, it can do the trick.

Where to See Your Readings

To see your sleep results, log in to the Fitbit app on your iOS or Android device and sync your Fitbit. The app that tracks your sleep is the same one you use to see your steps. You'll see a brief rundown of your results in the sleep tile.

You need to have slept at least three hours for Sleep Stages to work. It also doesn't work if you wear the tracker loose on your wrist or when it's running low on battery power.

To see your readings, tap the sleep time number to go to the sleep dashboard. From there, you can see each stage of sleep represented in a graph form that breaks down how much time you spent in each sleep stage and how close you were to your overall sleep goal for the day.

Scroll down to see your sleep results for the day and your average amount of sleep for the week. Tap any sleep section to bring up an hour-by-hour explanation of how you slept and which sleep stage you were in at a given time. The 30-day average and benchmarks show how your sleep compares with other people your gender and age.

Different Types of Sleep

For tracking, Fitbit worked with sleep researchers and the National Sleep Foundation to highlight four types of sleep, which you see in a readout in the morning when you wake up.

Here’s a breakdown, along with Fitbit's explanation, of what each stage means:


When it comes to being awake during the night, many of us think that waking up at all is bad news. It turns out that waking up during the night is a normal part of sleep. Waking up anywhere in the ballpark of 10 to 30 times in a single night is normal.

So, if you're one of those people who roll over a few times during the night or get up to use the bathroom once or twice, you're just like everyone else. There’s nothing to be worried about.

Light Sleep

Light sleep occurs when your body starts to slow down at night. It's that moment when you start to fall asleep, but you could be easily woken. The best example is those moments when you're commuting and fall asleep on the train or in the passenger seat of your coworker's car.

When you're in light sleep, you may be aware of what is going on around you, and someone can wake you up easily—but you're still asleep.

During this sleep stage, your heart rate decreases slightly from what it is when you're awake. Just because you can be woken easily doesn't mean this isn't a useful stage. Light sleep helps with mental and physical recovery, so you can feel better after an hour of light sleep than you did before you started to snooze.

Fitbit Sleep Stages screen


Deep Sleep

Deep sleep is the type of sleep you want to have each night. When you wake up in the morning and think, "Gosh, that was a great night of sleep," you probably had a lot of deep sleep during the night. When you're in a deep sleep, it's harder to wake you up than it is in light sleep. Your body becomes less responsive to stimuli, your breathing is slower, and your muscles relax.

During this sleep stage, your heart rate is regular, and your body starts to recover physically from the day. This stage also supports your immune system and can help with memory and learning. However, the older we are, the less deep sleep we typically get, although sleep patterns vary from person to person.


After you make it successfully through your first stage of deep sleep, you typically enter REM sleep. You stay in REM sleep for a longer period during sleep cycles that occur in the second half of the night. When you're in REM sleep, your brain becomes more active. In most cases, dreams occur during this stage. 

During REM sleep, your heart rate becomes more rapid, and your eyes move quickly from side to side. Muscles below the neck are typically inactive during this sleep stage, in part to prevent you from acting out what's happening in your dreams.

REM sleep helps with learning, regulating your mood, and memory. During this time, your brain also processes what happened during the day and consolidates your memories so they can be stored in your long-term memory.

How to Improve Your Readings

Unlike taking more steps to help you get fit, there's no apparent way to improve your sleep readings. During the week, Fitbit offers some suggestions on ways you can potentially improve those numbers.

  • Limit alcohol consumption: While consuming alcohol before bed may help you fall asleep, it can also contribute to you waking up during the night.
  • Create a regular bedtime and wake-up time: If having a regular bedtime and wake-up time is a challenge for you, set your Fitbit so that it reminds you to head to bed at the same time each night and then gently wakes you in the morning with a light vibration.

If you're routinely having trouble getting enough sleep, it's probably time to see a medical professional. The readings from your Fitbit may be useful to give your doctor a baseline idea of your problems before appropriate studies or treatments for you are recommended.

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