What should I know about Fitbit sleep stages?

While you're asleep, your body typically goes through several sleep cycles that last on average 90 minutes. Each cycle alternates between 2 types of sleep:

Light Sleep and Deep Sleep: With less brain activity than REM sleep, non-rapid eye movement (NREM) includes the stages of light sleep and deep sleep. Periods of deep sleep are typically longer early in the night.

Rapid Eye Movement (REM) Sleep: The stage associated with vivid dreams, REM sleep periods are typically longer as the night goes on (source).

Sleep stages are traditionally measured in a lab using an electroencephalogram to detect brain activity, along with other systems to monitor eye and muscle activity. Your Fitbit device can estimate your sleep stages in a more comfortable and convenient way.

Fitbit estimates your sleep stages by using your movement and heart-rate patterns. When you don't move for about an hour, your tracker or watch assumes you're asleep. Additional data such as the length of time when your movements indicate sleep behavior (like rolling over), help confirm your sleep status.

While you sleep, 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, it uses your movement and heart rate patterns to estimate your sleep cycles from the previous night.

Fitbit's sleep researchers and the National Sleep Foundation describe the following sleep stages. We've chosen these names for your Fitbit sleep log.

Light Sleep

Light sleep serves as your entry point into sleep each night as your body unwinds and slows down. This stage typically begins within minutes of falling asleep. During the early part of light sleep, you may drift between being awake and asleep, remaining somewhat alert and can be easily awoken. Your breathing and heart rate usually decrease slightly during this stage.

Light sleep promotes mental and physical recovery.

Deep Sleep

Deep sleep typically occurs in the first few hours of sleep. When you wake up feeling refreshed in the morning, you likely experienced solid periods of deep sleep the night before.

During deep sleep, you become harder to be awakened since your body becomes less responsive to outside stimuli. Your breathing slows down, your muscles relax and your heart rate usually becomes more regular. Adults often have a normal decrease in deep sleep as they age, though sleep patterns vary among individuals.

Deep sleep promotes physical recovery and supports aspects of memory and learning, as well as your immune system.

REM Sleep

The first phase of REM sleep typically occurs after you've had your initial stage of deep sleep. You generally spend a longer period in REM sleep during the sleep cycles in the second half of the night.

During this final stage of sleep, your brain becomes more active. Dreams mainly occur during REM sleep, and your eyes move quickly in different directions. Your heart rate increases, and your breathing becomes more irregular. In principle, muscles below the neck remain inactive to prevent you from acting out your dreams.

REM sleep has been shown to play an important role in 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.

The benchmark is based on published data to show how your sleep stage estimates from the previous night compare to the averages of others in the same age range and sex (source). The graph displays the typical range for each sleep stage as a shaded area. Keep in mind sleep cycles vary naturally, so you may notice your sleep data occasionally fall outside the typical ranges.

Another way to analyze your sleep stages is to compare your data from last night to your own 30 day average (under the 30 day average tab), since your sleep patterns may vary over time.

Your sleep stages data helps you track your patterns and notice variations. If you have any concerns about your sleep health, we recommend sharing the information with your doctor. The National Sleep Foundation 

offers additional valuable resources.

It's normal to have awake minutes in your sleep stages. You may not remember waking up since you likely fell right back to sleep, especially if you were awake for less than 2-3 minutes at a time. If you wake up in the morning feeling like you had a restless night, you may notice more awake minutes in your sleep stages as compared to other nights.

If you previously tracked sleep with Fitbit, your log showed the time spent awake, restless, and asleep. We fine-tuned our mechanism for tracking sleep to estimate your sleep stages by incorporating heart rate and other data. As a result, we combined your awake and restless time into total awake minutes to give you a clearer picture of your sleep cycles.

You may notice more awake minutes in your sleep stages than in your previous sleep data due to this change. If you're concerned about meeting your Fitbit goals, you can adjust your sleep goal to ensure you still achieve it. For instructions, refer to How do I track my sleep with my Fitbit device?

Note that the sleep sensitivity setting on your device doesn’t affect sleep stages. For more information, refer to How do I track my sleep with my Fitbit device?

Your device needs at least 3 hours of sleep data to estimate your sleep stages, so you won't find sleep stages for shorter naps.

Additionally, Fitbit offers several tools to help you sleep better. You can set a sleep schedule in the Fitbit app to maintain a more consistent sleep pattern. You can also explore your sleep habits through sleep insights and set a bedtime reminder in the Fitbit app to help you wind down each night. For more information, refer to How do I track my sleep with my Fitbit device?

For more information on sleep stages, check our blog posts REM, Light, Deep: How Much of Each Stage of Sleep Are You Getting? and Your Heart Rate Is the Key to Smarter Sleep Stages. Here's Why.

For additional sleep information including tips for feeling rested, visit the Fitbit blog.

When you set an alarm on Fitbit devices that support Smart Wake, turn on Smart Wake to avoid waking up while you're in deep sleep. Smart Wake attempts to find the best time to wake you, starting 30 minutes before your set alarm. It avoids waking you during deep sleep, increasing your chances feeling refreshed.

If Smart Wake can't find the ideal time to wake you, your alarm will alert you at the set time. For more information, refer to How do I manage alarms on my Fitbit device?