How does Fitbit track your sleep?

In this brief guide, we will answer the question “How does Fitbit track your sleep?” and discuss more “How Fitbit is useful in analysing your sleep quality?”

How does Fitbit track your sleep?

Just wearing your Fitbit to bed is enough for Fitbit to track your sleep. Just be sure to not wear the tracker too loose on your wrist or at low battery power.

Fitbit has built-in sensors that sense your movements, heart rate and oxygen saturation levels. There are also secret algorithms at work to more accurately estimate your sleep stage. For example, if you leave the watch by your bedside, it knows that you are not wearing it.

Fitbit makes use of heart rate and movement sensor readings to predict when you are asleep. For example, there is a good chance you are asleep if your heart rate is low and constant and your movement is limited.

A background on sleep study

In the medical field, an electroencephalogram (EEG) is used to measure sleep stages, which are basically small electrodes mounted onto the head and forehead. It measures brain activity by recording electrical activity on the scalp. An EEG is useful in diagnosing epilepsy, sleep disorders and brain tumours.

To carry out a proper sleep study an EEG test may be used in conjunction with a Polysomnograph. Polysomnography is a comprehensive test that records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study.

Polysomnography observes your sleep stages and cycles to identify if or when your sleep patterns are disrupted and why.

While the Fitbit is no replacement to an EEG or Polysomnograph, it does however track your heart rate and oxygen levels in the blood along with wrist movements to determine your sleep stages and cycles.

It can definitely be useful for someone trying to log their sleeping habits and help to make improvements as well. It would also be helpful to present a sleep log to your doctor if you are having trouble sleeping.

How do I view my sleep log data using Fitbit?

Download the Fitbit app on your iOS or Android phones. Sync your Fitbit device each morning to see last night’s sleep stats, including sleep score in the Fitbit app.

1.      In the Fitbit app, tap the Today tab which is the Fitbit logo in black.

2.      Tap the sleep tile Icon which has a purple moon with a Z next to it.

3.      Tap Today or another day to see details.

The science of how the Fitbit monitors sleep

Fitbit trackers track your heart rate variability along with heart rate when you are asleep. This helps differentiate between the different stages of sleep. The readings are obviously not very accurate from a medical point of view but it gives you basic information about your sleep patterns.

What is heart rate variability (HRV)

Heart rate variability or HRV is the variance in the time interval between consecutive heartbeats. Much like the difference between speed and acceleration, the Heart Rate Variability (HRV) is a measure of how the heart rate changes between different activity levels. Normally a heart does not have an even ticking interval like a clock. If looked closely, there is constant variation in between heartbeats in the order of milliseconds.

An easy way to sense your HRV is by feeling your pulse and taking a few deep breaths in and out. The interval between heartbeats becomes longer (heart rate slows down) when you exhale and shorter (heart rate increases) when you inhale.

Apart from breathing, HRV is considerably affected by exercise, stress, metabolic processes, cognitive processes and sleep. This makes HRV useful in distinguishing between the 4 stages of sleep.

How is Fitbit useful in analysing your sleep quality?

Fitbit has worked with sleep researchers and with the National Sleep Foundation to highlight the four stages of sleep. You can view the information on sleep stages by using the synchronizing the Fitbit app with your smartphone. The following are the four stages of sleep that the Fitbit will inform you of :


This is the awake sleep

betwixt state, where a person is consciously present as well as in a sleepy

state. This is a short period of 5 to 10 mins after which the actual sleep starts.

The light sleep: 

This is where the heart

rate starts to slow down and body temperature starts to drop a bit to adjust to the slower heart rate. This phase lasts about 15-20 mins and can extend to an hour in a not-so-good sleep.

The deep sleep: 

This is the state of sleep where if awoken from this stage a person feels disoriented, this stage is short and this is when the body is in its repair mode or maintenance. This lasts about 20-40 mins.

The REM sleep: 

This is called the Rapid Eye Movement stage of sleep. At this point, the heart rate and brain activity peaks overall and this results in the person seeing dreams.

This is a short period of 10 – 15 minutes but as the cycles of sleep progress, the REM sleep gets longer and can reach about 90 minutes.

Where to See Your Readings

To see the different stages of sleep go to Fitbit states to follow the steps below

1.      In the morning, open the Fitbit app and sync your Fitbit device.

2.      Tap the sleep tile. (If it says “Analyzing your sleep”, your device’s data hasn’t synced yet.)

3.      Tap Today (on Windows 10, tap Last Night).

4.      Tap the expand icon in the top right to open information about your sleep stages, and swipe to view your stats. Tap the icon again to close.

5.      Scroll down to view your time spent in each stage, and tap 30 Day Avg and Benchmark to view additional stats.

Visit the Fitbit site on how to adjust your tracker or more information on how to view sleep stats

How to improve your sleep?

Unlike a healthy diet to improve fitness, there is no sure-fire way to improve your sleep, but having a good diet and exercise routine is one way to improve your sleep. Apart from exercise, stress management will also help in improving the quality of your sleep.


In this brief guide, we answered the question “How does Fitbit track your sleep?” and discussed more on “How Fitbit is useful in analysing your sleep quality?”


Leave a Comment