Bedtimes
You are going to bed at 8:00pm. When should the alarm be?
Eight in the evening is an unusual hour to turn the light off, and almost everybody doing it has a reason. Either the morning starts before five, or the last few nights went badly enough that the body has stopped asking permission.
In short
If you go to bed at 8:00pm, set your alarm for 3:45am. 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. 5:15am gives you 9h and 2:15am still leaves you 6h.
- Alarm for a full night
- 3:45amAlarm 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 | 5:15am | 9h | Nine hours. Worth it if you are paying back debt, and more than most adults need every night. |
| 5 | 3:45amAim here | 7h 30m | The target most adults should hold on a normal week. |
| 4 | 2:15am | 6h | Six hours. Short, but a whole number of cycles, so you surface from a lighter patch. |
| 3 | 12:45am | 4h 30m | An emergency night. Fine occasionally, damaging as a pattern. |
An 8pm bedtime is either a schedule or a symptom
Very few adults have a body clock that wants to sleep at eight. The ones who genuinely do are at the extreme morning end of the chronotype distribution, and they tend to have been that way since childhood rather than having arrived there recently.
For everyone else, an 8pm bedtime is one of two things. It is a working schedule, built backwards from a start time before five in the morning, in which case it is a sensible piece of arithmetic and the rest of the evening has to be rearranged around it. Or it is recovery sleep after a stretch of short nights, which is your body taking back what it is owed and is worth letting it have.
- Falling asleep easily at 8pm on a normal week is a genuine morning-type signal
- Lying awake until 11pm after an 8pm lights-out is the opposite signal, and means the bedtime is too early rather than the sleep too short
- In summer this hour is fully light in most of the northern hemisphere, and light is the single biggest input to when melatonin arrives
The chronotype quiz at /chronotype-quiz runs the validated rMEQ and will tell you which of those two you are in about a minute.
Nine hours is not the target, and that matters here
From 8pm, six full cycles land you at 3:15am. That is nine hours of sleep, and for most adults it is more than the body actually wants on a normal night. The consensus figure from the American Academy of Sleep Medicine is seven or more, not nine or more, and sleeping well past what you need tends to leave you groggier rather than sharper.
So the useful row in the table below is usually the five-cycle one. From an 8pm bedtime that puts the alarm at 4:45am, which is seven and a half hours, and it is the row to aim at unless you are deliberately paying back a debt.
If you keep waking at 3am and then cannot get back down, the guide at /guides/why-you-wake-up-at-3am covers what is actually happening.
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 3:45am 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,3:45am 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 8pm?
For five full sleep cycles, which is seven and a half hours and the right target for most adults, set the alarm for 4:45am. Six cycles takes you to 3:15am and is nine hours, which is more than most people need. Both figures include the roughly fifteen minutes it takes to actually fall asleep.
Is 8pm too early to go to bed?
It is early, and whether that is a problem depends on whether you fall asleep. If you are asleep within twenty minutes or so, an 8pm bedtime is simply an early schedule and it is fine. If you spend an hour awake in the dark first, you are getting into bed before your body is ready and a later lights-out will get you more sleep, not less.
Why do I keep waking up at 3am after going to bed early?
Because from 8pm, 3am is seven hours in and the end of a full set of cycles. Your sleep pressure has largely been discharged by then, and the last stretch of the night is lighter and easier to surface from. If you are not tired at 3am, you may simply be sleeping the amount your body wanted from an earlier start.
Other bedtimes
The same arithmetic, run from a different 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 11:00pmWhere to put the alarm after a 11:00pm 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.
- Wake tonesAnnoying alarm soundsAn unbearable alarm tone works for roughly a week. After that you learn to silence it before you are properly conscious, and you are back where you started with a worse mood attached. The durable fix is not a harsher sound, it is making the alarm end somewhere your half-asleep self cannot reach.
- Head to headSleep Cycle vs SnoreLabIf someone in the bed has complained about your snoring and you want to test whether anything helps, SnoreLab. If you want a picture of the whole night and an alarm at the end of it, Sleep Cycle.
- FeaturesSmart wakeSmart wake is a 30 minute window before your alarm in which Tock watches for a lighter moment in your sleep and rings as soon as it finds one. If it never finds one, your alarm goes off at the exact time you set.
- Sleep soundsBinaural beatsA binaural beat is something your brain constructs when each ear receives a slightly different tone, so it exists only over headphones and vanishes the moment you use a speaker. The sleep evidence is limited, mixed and mostly short-term, and Tock does not include a binaural beats track, partly because sleeping in headphones brings problems of its own.
- Tock for youLight sleepersYou wake at everything, and then you are awake for forty minutes at 3am doing arithmetic on how much is left. By morning you cannot say what woke you, only that something did, several times.
- AlternativesTock vs SleepScoreSleepScore is the better pick if you want breathing and movement read contactlessly by a method you can have explained to you, and you already have an alarm you trust. Tock is the pick if you want one app that both tracks the night and wakes you, with playable audio of what it heard.
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 3:45am for a lighter moment and rings then, and your set time is always the fallback.