Sleep calculator
Wake up between sleep cycles, not halfway through one. Tell us when you need to be up, or when you are heading to bed, and we will do the counting.
Lights out at
11:15pm
5 cycles, 7 hours 30 minutes
- 9:45pm6 cycles9 hours asleep, 9 hours 15 minutes in bedA longer night
- 11:15pm5 cycles7 hours 30 minutes asleep, 7 hours 45 minutes in bedClosest to what adults need
- 12:45am4 cycles6 hours asleep, 6 hours 15 minutes in bedA short night
Most adults need 7 to 9 hours a night. We have added 15 minutes to fall asleep and counted in 90 minute cycles, which is a rule of thumb: real cycles vary from night to night, so the hours you get matter more than hitting a cycle exactly. A shorter night now and then is fine, just not every night.
The idea
Why cycles, not hours?
Through the night you move through light sleep, deep sleep and dreaming sleep, in cycles of roughly 90 minutes. Waking at the end of a cycle usually feels easier than being dragged out of deep sleep.
- About 90 minutesA rule of thumb for one sleep cycle. Real cycles vary between people and change through the night, so treat the times as a guide.
- About 15 minutesHow long most people take to drop off. We add it on, so your cycles start when you are actually asleep.
- 7 to 9 hoursWhat the NHS says most healthy adults need. That is 5 or 6 cycles, give or take.
How much sleep by age
| Age | Hours a night | Cycles we aim for |
|---|---|---|
| Adult, 18 to 64 | 7 to 9 | 5 |
| 65 and over | 7 to 8 | 5 |
| Teenager, 14 to 17 | 8 to 10 | 6 |
| Child, 6 to 13 | 9 to 11 | 7 |
Adult hours are from the NHS. Children, teenagers and over 65s use the National Sleep Foundation's 2015 expert panel ranges, which are for healthy people; some need a little more or less.
The working
How we work it out
Bedtime = wake up time − (cycles × cycle length) − time to drop off
Up at 7am and after 5 cycles? 5 × 90 is 7 hours 30 minutes. Add 15 minutes to fall asleep and you get lights out at 11:15pm. For 6 cycles, it is 9:45pm. We know. Ambitious.
Cycles usually run 90 to 110 minutes and vary from person to person and through the night, so you can pick your own length. With 100 minute cycles, the same 7am alarm and 5 cycles (8 hours 20 minutes) means lights out at 10:25pm. If you usually take 30 minutes to drop off, everything moves 15 minutes earlier again. Each option also shows the time in bed, because that is what your alarm sees.
Questions
Common questions
How much sleep do I need for my age?
The NHS says most adults need 7 to 9 hours. The National Sleep Foundation suggests 9 to 11 for children aged 6 to 13, 8 to 10 for teenagers and 7 to 8 from 65.
Are sleep cycles really 90 minutes?
Roughly, on average. They vary between people and through the night, so the cycle count is a rule of thumb and the total hours matter more.
Is 6 hours enough?
Now and then, you will cope. Most adults need 7 to 9 hours, and regularly getting less can affect your mood, focus and health.
Does a lie-in at the weekend make up for it?
A little, but a regular routine helps more. Going to bed and getting up at around the same time every day is one of the most useful things you can do.
What if I wake up in the night?
That is normal. Most people wake briefly between cycles and do not remember it. If you are lying awake for a long time most nights, it is worth talking to a GP.
Sources
- NHS Every Mind Matters: sleep problems
- Hirshkowitz M et al. National Sleep Foundation's updated sleep duration recommendations: final report. Sleep Health 2015
- NHS: insomnia
- IQWiG (InformedHealth.org): what is normal sleep? Cycles every 90 to 110 minutes
- NHS: how to get to sleep
Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.
When to talk to someone
See a GP if you have had trouble sleeping for 3 months or more, it is affecting your daily life, or you snore loudly and stop breathing in your sleep. A pharmacist can advise on short term help. If worry is keeping you up, Samaritans on 116 123 are there day or night.