Colin Snow
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person's overall health. Fitbit's sleep feature estimates sleep stages using a combination of movement and heart-rate patterns. While you sleep, your Fitbit device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV). These numbers fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, Fitbit uses movement and heart rate patterns to estimate sleep cycles from the previous night.
| Characteristics | Values |
|---|---|
| How it works | Fitbit uses an accelerometer and optical photoplethysmography (PPG) to measure bodily accelerations of the wrist and blood flow based on how green light from an LED on the back of the watch is reflected by the body. |
| Sleep stages | Fitbit can track light sleep, deep sleep, REM sleep, and time awake. |
| Sleep score | Fitbit gives a personalised sleep score based on heart rate, restlessness, time asleep, time spent in deep and REM sleep, and restoration. |
| Accuracy | Fitbit's sleep staging is correct in 30-second blocks slightly more than two-thirds of the time. There is a slight overestimation of REM from sensor readings, but the Fitbit algorithm corrects for this. |
| SpO2 sensor | Fitbit has a functional SpO2 sensor for measuring blood oxygenation, but it is not currently used by the Fitbit app. |
| Battery life | Fitbit has a robust battery life, lasting up to seven days. |
| Smart alarm | Fitbit has a smart alarm feature that wakes you during a light sleep stage within a 30-minute window before your set alarm time. |
What You'll Learn
Fitbit's sleep tracking features
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person’s overall health, playing a role in metabolic and emotional regulation, performance, and memory. Fitbit's sleep tracking features help users understand the impact of their sleep and learn how to get better rest, boost energy, and improve their well-being.
Fitbit's advanced sleep tools allow users to track their sleep each night and view trends over time. The heart rate sensors and motion detectors in Fitbit trackers and watches work behind the scenes to track sleep. Users can wear their tracker or watch to bed and view their sleep stats and insights in the app.
Fitbit devices track the beat-to-beat changes in the user's heart rate, known as heart rate variability (HRV). These numbers fluctuate as the user transitions between light sleep, deep sleep, and REM sleep stages. In the morning, when the user syncs their device, Fitbit uses movement and heart rate patterns to estimate sleep cycles from the previous night.
To help users improve their sleep, Fitbit offers bedtime reminders, silent alarms, and insights into how their sleep is related to their activity, mood, and other factors. Fitbit Premium provides additional tools, such as guided programs developed with sleep experts and a monthly personalized analysis of key sleep metrics.
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How accurate is Fitbit's sleep tracking?
Fitbit's sleep tracking uses a combination of motion tracking, heart rate monitoring, and machine learning to estimate your sleep duration and quality. While this may sound impressive, there are some limitations to the accuracy of Fitbit's sleep tracking.
Motion Tracking
Fitbits use accelerometers to detect movement during sleep. When you're in a deep sleep, you generally move less, while in REM sleep and lighter sleep stages, you tend to move more. However, this reliance on motion tracking can lead to inaccuracies. For example, it might interpret periods of restless sleep as periods of wakefulness or classify periods where you are awake but not moving as sleep.
Heart Rate Monitoring
Fitbits monitor your heart rate throughout the night to estimate periods of wakefulness. They track beat-to-beat changes in your heart rate, known as heart rate variability (HRV). These numbers fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. However, your heart rate can vary wildly, even during sleep. For example, your heart rate is likely to be higher if you exercise, eat a large meal, or drink alcohol before bed. As a result, Fitbit's heart rate sensors may struggle to accurately identify sleep stages.
Machine Learning
Fitbit uses a machine learning algorithm to analyse your movement and heart rate data, improving its ability to distinguish between different stages of sleep. The algorithm also takes into account additional factors such as your age, gender, and physical activity levels in its sleep estimation.
Research on Accuracy
Given the popularity of sleep trackers, there has been a lot of research exploring their accuracy, with a focus on Fitbit sleep trackers as they are the most common. These studies generally involve comparing the results of a Fitbit against a polysomnography, an extremely accurate way to measure sleep.
The research has found that Fitbit sleep trackers tend to overestimate total sleep time by about 10% and underestimate measures of deep sleep and REM sleep by about 20% each. As deep sleep and REM sleep are considered the most important for recovery and memory consolidation, this means your Fitbit may tell you your sleep is worse than it actually is.
A study comparing Fitbit with a professional scientific encephalography (EEG) found that Fitbit is 72-73% accurate, while the Oura ring v.2 is 59% accurate. Fitbit is almost 100% accurate for REM sleep and very close for deep sleep. However, it confuses some light sleep as being the awake phase.
Another study found that Fitbit Charge 6 accuracy against multichannel EEG placed on different brain areas showed that the Charge 6 is in a similar accuracy range as Charge 4/Charge 5 for deep, light, and REM sleep. The Charge 6 seems to have improved awake detection, with an accuracy of around 75%. Overall, the device still can't pass EEG accuracy, which is typically in the 82-85% range.
Limitations
While Fitbit sleep trackers can provide valuable insights into your sleep patterns, they have some limitations. They do not consider external factors such as room temperature, noise, or disturbances from partners or pets that can affect sleep quality. Additionally, determining sleep stages using motion and heart rate is a simplified approach, as sleep experts often use electroencephalography (EEG) and other advanced methods to precisely categorize sleep stages. Fitbit's algorithm lacks the depth of information provided by these methods.
Furthermore, there is evidence to suggest that the data provided by sleep trackers can increase sleep anxiety, making it harder to fall asleep. Instead of relying solely on sleep trackers, it is essential to focus on simple tips to improve sleep quality, such as sticking to a consistent sleep schedule, creating a relaxing bedtime routine, optimizing your sleep environment, and limiting screen time before bed.
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How does Fitbit's sleep tracking work?
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person's overall health. Fitbit's advanced sleep tools can help you get better rest, boost energy, and improve your well-being.
Fitbit trackers and watches use your sleeping heart rate, movement, and more to measure your time spent in each sleep stage and give you a personalized Sleep Score that shows how well you slept. While you sleep, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV). These numbers fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, Fitbit uses movement and heart rate patterns to estimate sleep cycles from the previous night.
Fitbit's sleep feature estimates sleep stages using a combination of movement and heart-rate patterns. When you haven't moved for about an hour, your tracker or smartwatch assumes that you're asleep. Additional data, such as the length of time of movements that are indicative of sleep behavior (such as rolling over), can also help confirm that you're asleep.
Each night, your body cycles through different sleep stages based on your heart rate, and getting enough time in each one is key to feeling refreshed. Light sleep strengthens memory and learning. Deep sleep enables physical recovery. REM sleep helps with strategic thinking and creativity.
To track your sleep with a Fitbit, simply wear your tracker or watch to bed. In the morning, sync your device to see your sleep stats and insights in the app. You can also set a silent alarm to wake up during the optimal stage of sleep.
While Fitbit's sleep tracking feature is generally accurate, it is important to note that it cannot accurately measure REM or deep sleep stages. For more precise measurements of these sleep stages, more sophisticated equipment, such as eye trackers or brain wave monitors, would be required.
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Fitbit's sleep tracking compared to other devices
Fitbit's sleep-tracking technology has improved over the years. Older Fitbit devices used wrist movement to track sleep, but now, heart rate monitoring is also used. This combination of heart rate and movement sensors is used to estimate sleep stages, giving you a breakdown of light, deep, and REM sleep (plus any awake time).
Fitbit's sleep feature assumes you are asleep when you haven't moved for about an hour. Additional data, such as the length of time of movements that are indicative of sleep behavior, can also help confirm that you are asleep. While you sleep, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV). These numbers fluctuate as you transition between light sleep, deep sleep, and REM sleep stages.
Fitbit's sleep tracking is generally considered accurate, with some studies showing that it is pretty accurate with sleep tracking. However, it is important to note that even the best sleep trackers can only manage around 80% accuracy compared to medical-grade sleeping equipment's assessments of sleep stages.
When compared to other devices, Fitbit's sleep tracking is considered to be more intuitive and varied. It offers solid activity tracking for all levels, wide-ranging food and calorie logging, integration with Fitbit smart scales, and room for plenty of health features. The data is easy to understand, and Fitbit's algorithms are intuitive and consistent.
Fitbit also has a feature called the Fitbit Sleep Score, which is a quick way to gauge your sleep. It is based on heart rate, the time spent awake or restless, and sleep stages. Most Fitbit users get a sleep score between 72 and 83.
In addition to sleep tracking, Fitbit also offers guided programs developed with sleep experts, such as "Habits for Restful Sleep" and "Get More Sleep," which are designed to help you improve your nighttime routine and work towards longer sleep.
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Improving sleep with Fitbit
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person's overall health, playing a role in metabolic and emotional regulation, performance, and memory. Fitbit's advanced sleep tools can help you get better rest, boost energy, and improve your well-being. Here are some ways to improve your sleep with Fitbit:
Understand Your Sleep
By tracking your sleep with a Fitbit device, you can gain insights into your sleep patterns and quality. Fitbit's sleep feature estimates sleep stages by combining movement and heart-rate patterns. It 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. Each of these sleep stages serves a different purpose, so understanding how much time you spend in each can help you identify and address sleep-related issues.
Set Sleep Goals and Create a Sleep Schedule
Use the Fitbit app to set sleep goals and create a sleep schedule with bedtimes and wake-up target times. Most adults need 7-9 hours of sleep per night, so the default goal is 8 hours. You can also set bedtime reminders to help you stick to your schedule, which is key to better rest.
Analyze Your Sleep Trends
View graphs of your sleep data in the Fitbit app to analyze your unique trends and discover potential changes you can make to improve your sleep. Compare your sleep trends to your activity levels, diet, and more to find patterns and make small adjustments as needed.
Optimize Your Sleep Environment
To improve your sleep quality, consider optimizing your sleep environment. This may include reducing exposure to blue light before bed by powering down your devices an hour beforehand. Additionally, creating a relaxing bedtime routine with activities like reading a book or listening to relaxing music can help you unwind and prepare for sleep.
Utilize Smart Wake
Take advantage of Fitbit's Smart Wake feature, which gently wakes you during a lighter sleep stage, helping you feel more refreshed in the morning. This feature is available on select Fitbit devices, including the Versa series and Ionic models.
Explore Fitbit Premium
Fitbit Premium offers more advanced sleep features, such as a detailed breakdown of your Sleep Score, guided sleep programs, and personalized sleep insights. These tools can provide specific guidance on improving your sleep habits and overall sleep quality.
By utilizing these features and tools, you can work towards improving your sleep quality, energy levels, and overall well-being with the help of Fitbit.
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Frequently asked questions
Fitbit uses a combination of movement and heart-rate patterns to estimate sleep stages. When the device hasn't detected movement for about an hour, it assumes that the user is asleep. Additional data, such as the length of time spent moving in ways indicative of sleep behaviour, help confirm that the user is asleep.
Fitbit's sleep staging is only correct about two-thirds of the time in 30-second blocks. However, there is no systematic bias in how it estimates the duration of light sleep, deep sleep, or sleeplessness. Therefore, using the app over multiple nights will give a good sense of sleep patterns.
Fitbit tracks light sleep, deep sleep, REM sleep, and time awake. Light sleep strengthens memory and learning, deep sleep enables physical recovery, and REM sleep helps with strategic thinking and creativity.
Fitbit's sleep tracking technology is more advanced than smartphone apps that use the accelerometer to track movement under a pillow. It combines wrist movement tracking with heart rate monitoring to make assumptions about sleep duration and stages.
The Google Pixel Watch 3 is considered one of the best Fitbit devices for sleep tracking, as it uses Fitbit's sleep algorithms and has a wider smart experience. The Fitbit Versa and Fitbit Charge 3 have also been mentioned as devices used for sleep tracking.
