Bedtimes
You are going to bed at 11:00pm. When should the alarm be?
Eleven is where most people actually turn the light off, whatever they intended. It works for a late start and quietly does not work for an early one, and the gap between those two is where most sleep debt in the world gets made.
In short
If you go to bed at 11:00pm, set your alarm for 6:45am. That is 7h 30m of sleep across 5 full cycles, plus the fifteen minutes it takes most people to actually fall asleep, so you wake at the end of a cycle rather than inside one. 8:15am gives you 9h and 5:15am still leaves you 6h.
- Alarm for a full night
- 6:45amAlarm for a full night5 cycles, 7h 30m asleep
- Length of an average sleep cycle
- 90 minLength of an average sleep cycleReal ones run 70 to 120
- Added before the first cycle
- 0h 15mAdded before the first cycleMost calculators forget this
| Cycles | Set the alarm | Time asleep | What it is good for |
|---|---|---|---|
| 6 | 8:15am | 9h | Nine hours. Worth it if you are paying back debt, and more than most adults need every night. |
| 5 | 6:45amAim here | 7h 30m | The target most adults should hold on a normal week. |
| 4 | 5:15am | 6h | Six hours. Short, but a whole number of cycles, so you surface from a lighter patch. |
| 3 | 3:45am | 4h 30m | An emergency night. Fine occasionally, damaging as a pattern. |
The bedtime people have, rather than the one they plan
Ask somebody what time they go to bed and they will often say ten. Watch what happens and it is usually eleven, because the evening runs over and the last thing takes longer than expected. That hour of drift is not a discipline failure so much as an accounting one: nobody plans the gap between deciding to go to bed and being asleep.
Eleven is fine if the alarm is at seven or later. Five cycles from here finishes at 7:45am, so a 7am alarm is about seven hours of sleep and a 7:45 alarm is seven and a half. It stops being fine the moment the alarm moves to six, which turns it into a six hour night, five nights a week.
- From 11pm, five cycles lands at 7:45am and four at 6:15am
- An 11pm bedtime with a 6am alarm is roughly six and a half hours, and it is the commonest structural deficit there is
- The drift between the intended bedtime and the real one is worth measuring before trying to fix it
A steady 11pm beats a variable 10pm
If you are picking between an eleven o clock bedtime you can actually hold every night and a ten o clock one you will hit three nights in five, take the eleven. Regularity does more work than duration at the margins, and the research on it is consistent enough to be worth acting on even though the headline advice is always about hours.
The reason is that the body clock is set by regularity rather than by totals. A schedule that moves around means the clock never settles, and the cost shows up as difficulty falling asleep and difficulty waking, which is exactly the pair of symptoms people try to solve by going to bed earlier.
The argument in full is at /blog/a-steady-schedule-beats-extra-sleep, and the measure Tock uses for it is at /glossary/sleep-regularity-index.
The table is an average, and your night is not
Ninety minutes is the number everybody quotes because it is roughly the mean. A real night does not run to it. Your first cycle tends to be short, the middle ones stretch, and by the last couple of hours you are cycling faster with more of each one spent in light sleep and REM. So the arithmetic above gets you to approximately the right alarm, and then the last half hour is a coin toss.
That coin toss is the entire argument for a smart alarm, and it is why this page ends with one rather than with a schedule. Tock spends the thirty minutes before 6:45am watching for the moment you are already stirring, on two channels: movement from the accelerometer and sound from the microphone. When it finds one it rings a little early. When it does not,6:45am rings exactly as you set it, so the fallback is never worse than a normal alarm. You can read the mechanism at how smart wake works, or start with sleep cycles explained if the arithmetic itself is the part you want to understand properly.
Questions people ask
What time should I wake up if I go to bed at 11pm?
Five full sleep cycles puts the alarm at 7:45am, which is seven and a half hours asleep. Four cycles is 6:15am at six hours. Both include the fifteen minutes or so it takes to fall asleep after the light goes off.
Is 11pm to 6am enough sleep?
It is about six and three quarter hours of sleep, which is under the seven hour figure the American Academy of Sleep Medicine gives for adults. It is survivable occasionally and it is a deficit as a pattern, and it sits mid-cycle, so the alarm is likely to catch you in a deep stretch.
Is going to bed at 11pm bad?
The hour is not the issue. An 11pm bedtime with a 7am alarm is a normal eight hours of opportunity and is completely fine. The same bedtime with a 5:30am alarm is a six hour night, and that is the version that causes problems, so the answer depends entirely on the other end.
Other bedtimes
The same arithmetic, run from a different lights-out.
- Going to bed at 8:00pmWhere to put the alarm after a 8:00pm lights-out.
- Going to bed at 8:30pmWhere to put the alarm after a 8:30pm lights-out.
- Going to bed at 9:00pmWhere to put the alarm after a 9:00pm lights-out.
- Going to bed at 9:30pmWhere to put the alarm after a 9:30pm lights-out.
- Going to bed at 10:00pmWhere to put the alarm after a 10:00pm lights-out.
- Going to bed at 10:30pmWhere to put the alarm after a 10:30pm lights-out.
- Going to bed at 11:30pmWhere to put the alarm after a 11:30pm lights-out.
- Going to bed at 12:00amWhere to put the alarm after a 12:00am lights-out.
- Going to bed at 12:30amWhere to put the alarm after a 12:30am lights-out.
- Going to bed at 1:00amWhere to put the alarm after a 1:00am lights-out.
- Going to bed at 1:30amWhere to put the alarm after a 1:30am lights-out.
- Going to bed at 2:00amWhere to put the alarm after a 2:00am lights-out.
- Going to bed at 3:00amWhere to put the alarm after a 3:00am lights-out.
Elsewhere on the site
A different corner of the same problem.
- Tock for youStudentsYou go to bed at a different time every night, set an alarm you already know you will sleep through, and you cannot just turn the volume up because there is someone asleep two metres away.
- AlternativesTock vs Apple Health SleepIf you wear an Apple Watch and you only want to see how long you slept, Apple Health already does it for free and does it better than any phone estimate. Tock adds the room: sound, snoring, a score, an alarm that can move earlier, and a coach that can explain what it found.
- RoundupsThe best sleep apps for studentsFor most students the best answer is free: the iPhone Clock app, a wake time you keep at weekends, and Alarmy's free tier if you sleep through things. Tock is the paid pick worth the money once you have tried that and still miss 9am lectures.
- Wake timesWaking up at 5:30amBedtimes by sleep cycle for a 5:30am alarm.
- Sleep by ageHow much sleep teenagers needThe American Academy of Sleep Medicine recommends that teenagers aged 13 to 18 years sleep 8 to 10 hours per 24 hours on a regular basis. The obstacle is a genuine biological shift: the adolescent circadian rhythm runs later, so a teenager cannot reliably fall asleep at the time an early school start requires.
- NapsThe 20 minute napA 20 minute nap is the standard recommendation because it produces a solid alertness benefit while ending before most people reach slow wave sleep, so you wake up clear rather than groggy. It is long enough to be worth the time and short enough to stay safe.
Tomorrow, you wake up just before your alarm
Setting the alarm on a cycle boundary is arithmetic and your night is not. Tock watches the half hour before 6:45am for a lighter moment and rings then, and your set time is always the fallback.