Sleep Efficiency: How to Calculate It and What It Means

Sleep efficiency is the percentage of your time in bed that you actually spend asleep. To calculate it, divide your total sleep time by your time in bed and multiply by 100. For example, 7 hours asleep out of 8 hours in bed is 87.5%. A sleep efficiency of 85% or higher is generally considered a sign of good sleep quality.

The sleep efficiency formula

Sleep efficiency (%) = total sleep time / time in bed x 100

• Time in bed runs from when you lie down to sleep until you get up for the day.
• Total sleep time is time in bed minus all the time you were awake: the time it took to fall asleep, time awake during the night, and any time lying awake before getting up.

Unlike total sleep alone, efficiency shows how much of your time in bed turns into sleep. Two people can both sleep 7 hours, but someone who needed 9 hours in bed to get there is sleeping less efficiently than someone who needed 7.5.

How to calculate sleep efficiency by hand: a worked example

Say your night looked like this:

1. Time in bed: 10:30 PM to 6:30 AM = 8 hours = 480 minutes.
2. Time awake in bed: 30 minutes falling asleep + 45 minutes awake during the night = 75 minutes.
3. Total sleep time: 480 - 75 = 405 minutes (6 hours 45 minutes).
4. Sleep efficiency: 405 / 480 x 100 = 84.4%.

Working in minutes avoids mistakes with fractions of an hour. If you also lay awake for 15 minutes before getting up, add that to the awake time.

What should count as "time in bed"?

If you read, scroll or watch something in bed before trying to sleep, that time inflates the denominator and makes your efficiency look worse than it is. Sleep researchers have pointed out this exact problem, so for a fair number, start the clock when you put the book or phone down and try to sleep, and stop it when you stop trying to sleep in the morning. Whatever rule you choose, use the same one every night so your numbers are comparable.

What is a good sleep efficiency?

A sleep expert panel convened by the National Sleep Foundation agreed that a sleep efficiency of 85% or higher indicates good sleep quality across age groups. The same panel also pointed to other signs of good sleep: falling asleep within about 30 minutes and not spending long stretches awake during the night.

• 85% or higher: generally considered good.
• Below 85% on most nights: you are spending a meaningful amount of time awake in bed. Look at whether the problem is falling asleep, staying asleep or waking too early.

Efficiency is one number among several. A very high figure paired with feeling exhausted every day can mean you are not giving yourself enough time in bed at all. Most adults need at least 7 hours of sleep a night.

How to track it: sleep diary or wearable

A sleep diary is the simplest method and the one sleep clinicians often use. Each morning, write down when you got into bed, roughly when you fell asleep, how long you were awake during the night, and when you got up. Estimates are fine. After one to two weeks, average the nightly results.

A wearable such as Apple Watch records time asleep and time awake automatically. It is convenient and consistent, but it estimates sleep from movement and heart rate, so it can miss some quiet time awake. Use it for trends, and cross-check with how you feel.

How to improve sleep efficiency

Most of the gains come from habits recommended by the American Academy of Sleep Medicine and the NHS:

• Keep a fixed wake-up time, including weekends. A regular schedule makes it easier to fall asleep at night.
• Go to bed when you feel sleepy, not just because it is a certain time.
• Get out of bed if you cannot sleep. If you are still awake after about 20 minutes, go and do something quiet in dim light, away from screens, then return when sleepy.
• Keep the bed for sleep. Moving reading and scrolling elsewhere helps your brain link bed with sleeping.
• Wind down for the last hour and turn off screens at least 30 minutes before bed.
• Avoid caffeine in the afternoon and evening, and avoid alcohol and large meals close to bedtime.
• Reduce fluids before bed to cut down on bathroom trips.
• Avoid sleeping in after a bad night and skip long daytime naps, which can make the next night harder.
• Keep the bedroom dark, quiet and comfortable.

Caffeine is a common hidden cause of a long time to fall asleep. Our caffeine and sleep guide covers timing in more detail.

When low sleep efficiency needs a professional

If you have had trouble falling or staying asleep for several weeks or months, or poor sleep is affecting your daytime life, talk to a doctor. Ongoing insomnia is common and treatable.

The American Academy of Sleep Medicine recommends cognitive behavioural therapy for insomnia (CBT-I) as a treatment for chronic insomnia in adults. CBT-I is a structured programme delivered by trained clinicians, such as sleep psychologists or specially trained therapists, sometimes through a supervised online course. Some parts of it involve temporarily changing how much time you spend in bed, which makes you sleepier at first and is not suitable for everyone, so it should be done with professional guidance rather than on your own. If insomnia is a problem for you, CBT-I is worth asking your doctor about.

Also see a doctor if you snore loudly, have been told you stop breathing or gasp during sleep, or feel very sleepy during the day despite enough time in bed.

Seeing your nights in FitRest

FitRest reads your sleep from Apple Health and shows each night's time asleep, time awake and disruptions, with your sleep quality, consistency and trend over time. Sleep vs target shows how each night compares with the sleep goal you set. If you keep a sleep diary alongside it, you can use the times shown to run the calculation above. Learn more on the sleep tracking page.

Sources

• Ohayon et al. (2017), Sleep Health - National Sleep Foundation's sleep quality recommendations
• Reed and Sacco (2016), Journal of Clinical Sleep Medicine - Measuring Sleep Efficiency: What Should the Denominator Be?
• Edinger et al. (2021), Journal of Clinical Sleep Medicine - Behavioral and psychological treatments for chronic insomnia disorder in adults: an AASM clinical practice guideline
• American Academy of Sleep Medicine - Cognitive Behavioral Therapy
• American Academy of Sleep Medicine - Healthy Sleep Habits
• NHS - Insomnia