How FitBit Tracks Sleep: Understanding The Sleep Stages Feature

How To Track Your Sleep Using Your Fitbit

Fitbit Sleep Stages screen
Fitbit Sleep Stages.

There are tons of different devices to help you track how you sleep, of course, and some fitness trackers, including a number of Fitbit models, can get the job done as well. Not all sleep is created equally, however. Sleep Stages, a Fitbit feature, is designed to help you get your best sleep.

Some Fitbit trackers can tell you not only how long you were actually asleep, but what type of sleep you were likely getting while you were under the sheets. Curious how it works? Here’s a rundown on the feature and how to understand the different sleep stages that it tracks.

Which Device Do I Need?

In order for you to take advantage of Sleep Stages, you need to be using a device that supports it. For now, that’s specifically Fitbit trackers that already track your heart rate, specifically the Fitbit Alta HR, Fitbit Blaze, and Fitbit Charge HR. These are all wrist-worn trackers, and you’ll need to keep them on for the whole night – that means from when you head to bed until when you wake up in the morning – in order for the feature to work.

How Does Fitbit Know I'm Sleeping?

If you were to go to a doctor for a sleep study, your sleep stages would be measured by an electroencephalogram, which would pay attention to your brain activity. You’d also likely be hooked up to other machines that monitor your muscle movements.

While your Fitbit is definitely not a replacement for going to see a sleep specialist, it detects some of the same things by monitoring your heart rate and your movement while you’re sleeping (or attempting to sleep). Using those measurements, it’s able to make some reasonable guesses. For instance, if your heart rate remains about the same and you don’t move for an hour, then chances are good you’re asleep.

Fitbit is able to monitor your heart rate variability (HRV) while you sleep, which helps it determine when you’re moving between different levels of sleep. The ratings you get aren’t going to be quite as robust as what you might get from a doctor, but if you’re looking for just some basic information about yourself and how you slept last night then it can do the trick. 

Where To See Your Readings

In order to see your specific sleep results, you’ll need to log into the Fitbit app and sync your device – that means you’ll need to have the app installed on your iOS or Android device. The app to track your sleep is the same one you use to see your steps. When you do, you’ll see a brief rundown of your results in the sleep tile.

Tip: You’ll need to have slept at least 3 hours in order for Sleep Stages to work. It also won’t work if you happen to wear your tracker loose on your wrist, or if it’s running super low on battery power.

If you want to see exactly what your readings are, tap on that sleep time number to go to the sleep dashboard. From there, you’ll be able to see each stage of sleep represented in a graph form breaking 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, and you’ll see your individual sleep results for the day, as well as your average amount of sleep for the week. You can tap on any specific sleep section you want to bring up an hour-by-hour explanation of how you slept and what sleep stage you were in at a given time. You can also tap into details such as your 30-day average and benchmarks for how your sleep compares to other people your gender and age.

Different Types of Sleep

For the purposes of tracking, Fitbit worked with sleep researchers and the National Sleep Foundation to decide to highlight four specific types of sleep. These are what you’ll see in a read out in the morning when you wake up.

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

Awake: When it comes to being awake during the night, many of us think that waking up at all is bad news. Turns out, waking up during the night is a really normal part of sleep. In fact, waking up anywhere in the ballpark of 10-30 times in a single evening is perfectly normal.

So, if you’re one of those people that roll over a few times during the night, or even gets up to pee once or twice, you’re just like everyone else. There’s nothing to be super worried about.

Light Sleep: Light sleep is 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 up again. The best example is probably those moments when you’re commuting and fall asleep on the train or in the passenger seat of your co-worker's car. When you’re in light sleep, you might still be aware of what is going on around you, and someone could wake you up pretty easily – but you’re still asleep.

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

Sleep Stages graph
Sleep Stages tracks your sleep through four stages.  Fitbit

Deep Sleep: Deep sleep is the type of sleep you really 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 ton of deep sleep during the night. When you’re in a deep sleep, as you can imagine, it’s harder to wake you up than it is in a period of light sleep. Your body becomes less responsive to stimuli, your breathing becomes slower, and your muscles start to relax. 

During this sleep stage, your heart rate becomes more regular and your body starts to recover physically from the day before. This stage also helps support your immune system and can help with memory and learning. Unfortunately, the older we get, the less deep sleep we typically get, although sleep patterns vary from person to person.

REM: Once you’ve made it successfully through your first stage of deep sleep in an evening, you typically enter REM sleep. You typically stay in REM sleep for a longer period of time during sleep cycles occurring 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 will 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 the day before, 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 obvious way for how you can improve your sleep readings. During the week, however, Fitbit does offer 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, you can set your Fitbit up so that it reminds you to head to bed at the same time each night, and then gently wakes you up in the morning with a light vibration.

If you’re routinely having trouble getting enough sleep, then it’s probably time to go see a medical professional. Your readings from your Fitbit can likely be a helpful tool for your doctor to look at and get a baseline idea of what your issues are, so he or she can recommend appropriate studies or treatments for you going forward.