Sleep efficiency: how to calculate it, and how to read the number

Sleep efficiency is the percentage of your time in bed that you actually spend asleep. In CBT-I (cognitive behavioral therapy for insomnia), it is calculated from a sleep diary and used to review your sleep schedule.

The formula

Sleep efficiency (%) = time asleep ÷ time in bed × 100

Time asleep = time in bed − (time to fall asleep + time awake during the night + time between final awakening and getting up)

Worked example

Item	Value
In bed / out of bed	23:00 to 7:00 (time in bed 8 hours = 480 minutes)
Time to fall asleep	60 minutes
Awake during the night	30 minutes
Final awakening to getting up	30 minutes
Time asleep	480 − 120 = 360 minutes (6 hours)
Sleep efficiency	360 ÷ 480 × 100 = 75%

How to read it

• A low number means you spend a lot of time awake in bed. CBT-I's stimulus control aims to reduce time spent awake in bed, so the bed is linked with sleeping again.
• Look at the average over one to two weeks, not a single night.
• Raising the number is not a goal in itself. Sharply limiting time in bed (sleep restriction) has been reported to cause strong daytime sleepiness in the first weeks. Don't do it on your own; do it with a clinician.

Getting the numbers from your diary

You need the time you got into and out of bed, how long it took to fall asleep, and how long you were awake at night. Nyxtune lets you log these each morning with rough estimates. See also how to keep a sleep diary.