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What time should I go to bed? Work back from your wake-up time
What it does
Go to bed at the time that gives you seven to nine hours before the alarm, plus however long you take to fall asleep. Count back from your wake-up time rather than forward from when you feel tired. The alarm is the fixed point, and the body clock learns the morning.
- Put in your weekday alarm The one work sets, not the one you would like. The alarm is the fixed point.
- Pick the hours and your drop-off time Seven and a half if you do not know. If you often lie there, allow 30 and treat that as its own problem.
- Hold the alarm for seven mornings Judge it by the afternoons after a fortnight, not by the first morning.
Most people do the sums backwards. It goes like this: you're still up, the phone says 11.20pm, and you tell yourself you'll be asleep by midnight. Midnight to 6.30 is six and a half hours, which sounds nearly fine, so you give it another twenty minutes.
Then the alarm, at 6.30. The 11.20 was really 11.50, the midnight was really 12.25, and the six and a half hours was five and a bit. You do the sum again at 7.15, standing in the kitchen, and it comes out worse.
That's doing the maths forwards, from a bedtime you pick in the moment. It isn't a character flaw. It's the only way anyone can do it when the fixed point is at the wrong end of the night.
What you lose is the next evening: too tired at 8pm to do anything useful, too wired by 11 to go up. Which is where this started.
Why the wake-up time is the fixed point
Sleep pressure and the body clock decide between them when you sleep, and how to fall asleep and stay asleep explains both. For bedtime, it's the clock that counts.
The US National Institute of Neurological Disorders and Stroke describes light as perhaps the greatest influence on when you sleep. You can't choose a bedtime and expect the clock to follow it. You can choose a wake-up time, and the clock follows that, because getting up is when your day's light begins.
Regularity matters as much as the hours. A 2024 study in the journal Sleep followed 60,977 UK adults who'd worn a wrist monitor for a week.
Compared with the least regular fifth, the most regular fifth had about a 30% lower risk of dying over the next six years. Regularity predicted this better than how long people slept.
That's an association in a large group rather than a promise to you, and a strong reason to pick a wake-up time you can keep.
Then there are the cycles. Through the night you move in rounds between non-dreaming sleep, which starts light and goes deep, and dreaming sleep. Most of the deep sleep comes in the first half of the night, and the first dreaming period arrives about 90 minutes in.
So the sum runs backwards. The hours go in first; the bedtime is what's left.
How to work out your bedtime
- Start from the wake-up time you already have. Work sets the weekday alarm for most of us, and that's the fixed point. What Saturday does with it is the only real decision: the same time, or an hour later at most. The NHS advice is to get up at the same time every day, and that study of 60,977 people is the reason why. If you want the case in full, read why your wake-up time matters more than your bedtime.
- Pick your hours. The NHS puts adult sleep need at seven to nine hours. If you don't know where you sit in that range, start at seven and a half. Judge it by how the afternoons feel after a fortnight, not by how the first morning feels.
- Add the time it takes you to fall asleep. Time in bed isn't time asleep. If you usually drop off without a fight, allow 15 minutes. If you often lie there, allow 30, and see that as a separate problem to solve. When people don't know, we plan on 15.
- Do the sum. Wake-up time, minus hours, minus falling asleep. For a 6.30am alarm and seven and a half hours, that's 11pm asleep and lights off at 10.45pm. The worked example below runs the same sum in cycles.
- Count the wind-down back as well. The NHS suggests relaxing for at least an hour before bed, so for lights off at 10.45 the quiet hour starts at 9.45pm. What goes in that hour is covered in how to wind down before bed.
- Hold the wake-up time when the night goes wrong. The NHS advice after a bad night is not to sleep in but to stick to your regular hours. The pressure to sleep builds with every hour awake, so the repair happens the next night, as long as you don't move the morning.
The worked example, in cycles
A sleep cycle is one round of light, deep and dreaming sleep. It's usually quoted as 90 minutes. Five of those is seven and a half hours.
So: alarm at 6.30am. Five cycles back is 11pm.
Add 15 minutes to fall asleep and the light goes off at 10.45pm. Add the quiet hour and you start winding down at 9.45pm.
The caveat is that 90 is an average, not a measurement of you. Harvard Medical School's sleep division puts the first cycle at 70 to 100 minutes and later ones at 90 to 120. Your own vary with age, stress, illness and how well you slept the night before.
Yours might end at 6.05am or 7.10am, so the cycle sum checks the hours rather than setting the alarm.
What the maths can't do
It can't tell you how you'll feel when the alarm goes. The popular idea is that waking at the end of a cycle avoids the grogginess.
A 2019 review of sleep inertia, the name for that grogginess, found the evidence on whether the stage of sleep at waking matters is mixed. What it is clear on is that the grogginess fades over 15 to 30 minutes and is worse after a short night.
So the sum protects the hours. How you feel at 6.30 is mostly decided by the week before it.
If the sum says 10.45pm and you're never asleep before 1am, the problem isn't the arithmetic. Start with the sum alone anyway: pick the alarm, count back, and keep that alarm for seven mornings before you decide anything else.
Read next
Better sleep
How to fall asleep and stay asleep
The evening
Why your wake-up time matters more than your bedtime
The evening
How to wind down before bed
Questions
What is a good bedtime?
The one that's seven to nine hours, plus the time you take to fall asleep, before an alarm you keep every day. For a 7am alarm that's somewhere between 9.45pm and 11.45pm. There's no good bedtime in the abstract, only a good one for your morning.
What does a healthy sleep schedule for an adult look like?
One with the same wake-up time all week and a bedtime that moves by no more than an hour either side. For example: up at 6.30 every day, winding down from 9.45pm, lights off at 10.45pm, and the Sunday lie-in stops at 7.30. The 2024 study above found the regular pattern mattered more than the exact number of hours.
Does the clocks going back change the sum?
Only for a few days. Your alarm moves an hour while your body clock takes its time catching up, which is why the first week of November feels odd. The wake-up time stays the anchor; the clocks go back covers how to move it.
Sources
- Insomnia, NHS, 2024
- Fall asleep faster and sleep better, NHS Every Mind Matters, 2026
- Brain basics: understanding sleep, National Institute of Neurological Disorders and Stroke, 2025
- Science of sleep: what is sleep?, Harvard Medical School Division of Sleep Medicine, 2021
- Sleep regularity is a stronger predictor of mortality risk than sleep duration: a prospective cohort study, Sleep, 2024
- Sleep inertia: current insights, Nature and Science of Sleep, 2019
This article is general information, not medical advice. If sleep problems last more than a few weeks, speak to your GP.
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