What time to go to bed
Set the time you have to be up. Every bedtime here is a whole number of sleep cycles before it, with time allowed for falling asleep, and both of those numbers are on the page for you to change.
Go to bed at 10:15 pm
5 cycles and 7h 30m asleep: the row nearest eight hours.
| Get into bed | Cycles | Time asleep |
|---|---|---|
| 8:45 pm | 6 cycles | 9h |
| 10:15 pm | 5 cycles | 7h 30m |
| 11:45 pm | 4 cycles | 6h |
| 1:15 am | 3 cycles | 4h 30m |
7h 30m asleep
The same night on a clock face, read the usual way round.
The two assumptions
Move either one and every time above moves with it. The settings follow you around the site.
Common wake times
All 96 wake timesOther calculators
Shift rota planner
Days, nights and days off, one letter a day: where whole cycles of sleep fit between the shifts, commute and switch days included, with a calendar file to take away.
If I sleep now
The same sum run forwards from the clock where you are, for when the alarm is the part you have not decided yet.
Nap lengths
Twenty minutes, thirty, an hour, or one whole cycle, and what time each of them puts you back on your feet.
Travel planner
What your bedtime becomes in another zone, and a night-by-night plan to walk it across, before you fly or after you land.
Find your cycle
A notebook of your own mornings, kept on your device, and the cycle length from 70 to 120 minutes that fits them best.
The clocks go forward
14 March 2027 in the United States, 28 March in the UK and EU: a bedtime walked across the missing hour a step at a time.
The week's tally
Seven nights against a target you set: the sleep debt sum, done as a subtraction, kept on your own device and sent nowhere.
How it works
Sleep calculators rest on a convention: that sleep runs in cycles of about ninety minutes, and that an alarm is best set for the end of one. This site takes the convention as given and does the arithmetic. It multiplies the cycle, subtracts the result from your alarm, and prints what comes out. The reference page on cycle boundaries says what the convention rests on and what it does not show.
It is arithmetic. It is not a measurement of you, it does not know how tired you are, and it is not medical advice. A real cycle is not ninety minutes on the dot, it changes across a night and between people, and nobody here has measured yours — which is exactly why the ninety is a slider and not a secret. The reference pages set out where the number came from and what it cannot tell you.
Free, no account, nothing to sign up for. Nothing you type is sent anywhere.