Bedtimes

You are going to bed at 9:30pm. When should the alarm be?

Half past nine is the bedtime almost every piece of sleep advice assumes without saying so. It is what "get eight hours before a seven o clock start" actually means once you count the time it takes to fall asleep.

If you go to bed at 9:30pm, set your alarm for 5:15am. 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. 6:45am gives you 9h and 3:45am still leaves you 6h.

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Alarm for a full night: 5:15amAlarm 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

Wake times for a 9:30pm bedtime, counted forwards in whole sleep cycles.
Cycles	Set the alarm	Time asleep	What it is good for
6	6:45am	9h	Nine hours. Worth it if you are paying back debt, and more than most adults need every night.
5	5:15amAim here	7h 30m	The target most adults should hold on a normal week.
4	3:45am	6h	Six hours. Short, but a whole number of cycles, so you surface from a lighter patch.
3	2:15am	4h 30m	An emergency night. Fine occasionally, damaging as a pattern.

Counted forwards from 9:30pm in 90 minute cycles, with 15 minutes added at the start for the time it takes to actually fall asleep. Most bedtime calculators leave that quarter of an hour out, which is how they end up telling you to be asleep at the moment you are getting into bed. Real cycles run anywhere from about 70 to 120 minutes and change length through the night, so treat this as a starting point rather than a schedule.

The bedtime hidden inside most sleep advice

Advice about sleep tends to arrive as a duration rather than as a time, which quietly skips the hardest part. "Eight hours before a 7am alarm" sounds like an 11pm bedtime and is not: you are not asleep when the light goes off, and eight hours of sleep needs roughly eight and a quarter hours of bed. That puts lights out at about 9:30pm, and stated that way it is a much bigger ask.

This is also close to the midpoint of the adult chronotype distribution. Most people can fall asleep at 9:30 without much difficulty if the evening before it was dim, which is what makes it the realistic version of the advice rather than the theoretical one.

From 9:30pm, five cycles lands at 6:15am and six at 4:45am
Eight hours of sleep needs more than eight hours of bed, and the gap is where most schedules go wrong
A 7am alarm on a 9:30pm bedtime is a genuine eight and a half hours of opportunity

The fifteen minutes most calculators leave out

The table on this page adds fifteen minutes between lights out and the first cycle starting, and most bedtime calculators do not. That omission is why so many of them are quietly optimistic: they tell you to go to bed at the moment you would need to already be asleep, so every night comes in a quarter of an hour short and the deficit compounds across a week.

Fifteen is an average and yours may differ. Consistently taking more than about thirty minutes to fall asleep is worth paying attention to, and consistently taking under five usually means you are going to bed short rather than falling asleep well.

The term is sleep latency, and it is set out at /glossary/sleep-latency.

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 5:15am 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,5:15am 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

If I go to bed at 9:30pm what time should I wake up?

Five sleep cycles puts your alarm at 6:15am, which is seven and a half hours asleep. Six cycles takes you to 4:45am at nine hours, and four cycles to 7:45am at six. Each of those adds fifteen minutes for falling asleep.

Is 9:30pm too early for a bedtime?

Not if your alarm is before seven. A 9:30pm lights-out and a 6:30am alarm is eight and three quarter hours of opportunity, which is a comfortable night rather than an excessive one. It only becomes too early if you are still awake at eleven, which means the hour is ahead of your body clock.

How much sleep is 9:30pm to 6am?

About eight and a quarter hours in bed, and roughly eight hours asleep once you subtract the time it takes to drop off. That is between five and six full sleep cycles, so a 6am alarm will often land you mid-cycle, which is exactly the case a smart alarm exists to fix.

Other bedtimes

The same arithmetic, run from a different lights-out.

Elsewhere on the site

A different corner of the same problem.

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 5:15am for a lighter moment and rings then, and your set time is always the fallback.

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