Free tool
Sleep Efficiency Calculator
Sleep efficiency is the single most useful number in insomnia treatment, and almost nobody knows theirs. Enter last night's times and you'll have it in about a minute — calculated the way a sleep clinic calculates it.
Everything runs in your browser. Your entries stay on your device, and you don't need an email address to see your result.
1 Last night
Estimates are fine — nobody watches the clock accurately at 3 a.m., and the protocol doesn't need you to.
2 A short safety check
This decides whether it's appropriate for us to suggest a sleep schedule at the end — not whether you get your numbers. You get those either way.
Your night, broken down
What to do with this
Your diary
| Night | In bed | Asleep | Efficiency |
|---|
See a doctor rather than a website if:
- Anyone has seen you stop breathing, gasp or choke in your sleep. Untreated sleep apnoea does not respond to schedule changes, and restricting sleep on top of it makes it worse.
- You fall asleep without intending to during the day — particularly at the wheel.
- You physically act out dreams. This has recognised medical significance and is worth investigating properly.
- Sleep loss is affecting your mood to the point that you feel unsafe, or you are having thoughts of harming yourself.
- You are taking a prescribed sleep medication. Changing your schedule around it is a conversation to have with whoever prescribed it.
Get the printable 7-night diary
One night is a snapshot. Seven is a pattern you can act on — and it's what a clinician would ask you to bring. We'll build you a printable diary with your figures already on it, so you can fill in the rest by hand and see your real average.
Ready to print
Your baseline night is filled in on row one, with six blank rows to go. Keep it by the bed and complete it first thing, not at 3 a.m.
Why this number matters more than hours slept
Ask someone with insomnia how they slept and you'll get a figure in hours. It's the wrong measurement, because it treats a night in which you slept six hours out of six and a half as identical to one where you slept six out of ten. Those are completely different problems and they need opposite solutions.
Sleep efficiency captures the difference. It is total sleep divided by total time in bed. Somebody at 92 percent is sleeping about as densely as a person can; if they're tired, they need more opportunity, not better technique. Somebody at 65 percent is spending three or four hours a night lying in the dark not sleeping — and that time is not neutral, because it is teaching them, night after night, that bed is a place where you lie awake.
The counterintuitive fix
The instinct when you're not sleeping enough is to go to bed earlier and allow more time. It reliably makes things worse: a longer window spreads the same amount of sleep more thinly, efficiency drops further, and the association between bed and wakefulness gets stronger.
The approach with the strongest evidence behind it does the opposite. Sleep restriction — better described as sleep window compression — temporarily shortens your time in bed to match the sleep you're actually getting, then widens it back out as efficiency climbs. Sleep becomes deeper and more continuous because the pressure to sleep is concentrated rather than spread out. It is the most effective single component of cognitive behavioural therapy for insomnia, which is the recommended first-line treatment for chronic insomnia in adults ahead of medication.
It is also genuinely demanding for the first week or two, and it is not right for everyone — which is why this page asks a few questions before suggesting a window, and why it won't suggest one at all if your answers point somewhere else.
Getting an accurate reading
- Fill it in during the morning, not overnight. Clock-watching at 3 a.m. is itself a sleep problem.
- Estimate. Nobody knows precisely how long they lay awake, and the protocol has never needed them to.
- Count time in bed from getting in to getting out — including the reading, the phone, and the lying there afterwards.
- Log a full week before you change anything. A single bad night is not a pattern.
Related reading
Common questions
What is sleep efficiency?
It is the share of your time in bed that you actually spend asleep, written as a percentage. Eight hours in bed with seven hours of sleep is 87.5 percent. It matters because it separates two problems that feel identical at three in the morning: not getting enough sleep, and spending too long in bed trying. The second is far more common in long-running insomnia, and it responds to a completely different approach.
Where does the 85 percent figure come from?
It is the conventional threshold used in cognitive behavioural therapy for insomnia. Below roughly 85 percent, the time you are allowing for sleep is longer than the sleep you can currently produce, and the surplus gets spent lying awake — which is exactly the association your brain then learns. Above about 90 percent the window may be too tight. Between the two is where clinicians generally aim.
Why does one night not give me a sleep window?
Because a single night is noise. Sleep varies enormously from night to night, and a protocol built on your worst night in a fortnight would prescribe a window far too short. Clinicians work from about a week of diary entries. This tool will show you a provisional figure after one night and a real one once you have logged five, and it keeps your entries in your own browser so you can build that week up.
Is my data stored anywhere?
Your diary entries are saved in your own browser using local storage. They are not sent to us and we cannot read them. Clearing your browser data will remove them. If you enter your email for the printable diary we receive your name and email — nothing else.
Why did the tool refuse to give me a sleep window?
Two reasons are possible. Either you ticked something that points at a sleep disorder needing diagnosis rather than a schedule change — untreated sleep apnoea is the big one, and restricting sleep on top of it makes things worse — or you ticked a condition where deliberately shortening sleep needs a clinician's supervision, such as bipolar disorder or epilepsy. In both cases you still get your numbers; what is withheld is a self-directed instruction that would not be safe to follow.
Should the sleep window include naps?
During an active sleep restriction protocol, naps generally come out, because they reduce the sleep pressure the approach depends on. Older adults and people with certain medical conditions are sometimes advised differently. If you nap regularly and are unsure, that is worth raising with your doctor.
If your efficiency is low and the wakeups are the problem
Compressing your sleep window is step one. End 3AM Wakeups is our 21-day programme for the rest of it — what to do when you're awake at three, how to stop the 4 a.m. dread loop, and how to widen the window back out without losing the gains.
Educational guidance, not medical treatment. Chronic insomnia deserves a conversation with your doctor.