Going to bed right now?
We'll tell you the best times to set your alarm for.
A good night's sleep is usually 5–6 complete 90-minute cycles. Waking at the end of a cycle, rather than mid-cycle, is what helps you feel refreshed.
How the sleep calculator works
Sleep runs in cycles of roughly 90 minutes. Across each one you pass from light sleep down into deep slow-wave sleep and back up into REM, and the balance shifts as the night goes on — deep sleep fills the first couple of cycles, while REM periods lengthen towards morning.
Waking in the middle of deep sleep is what produces that heavy, disoriented feeling that can take half an hour to shake off. Waking near the end of a cycle, in lighter sleep, is considerably easier. This calculator counts in 90-minute blocks from your chosen time and adds about 15 minutes for falling asleep, so the times it gives you are more likely to land near a cycle boundary.
One honest caveat: 90 minutes is an average. Real cycles run from about 70 to 120 minutes and vary between people and between nights, so treat the results as good candidate times rather than a precise forecast. Total sleep matters more than cycle timing — it is never worth cutting an hour off your night to hit a neat number.
How much sleep do you need?
| Age | Sleep needed |
|---|---|
| Toddlers (1–2 years) | 11–14 hours |
| Preschoolers (3–5 years) | 10–13 hours |
| School age (6–13 years) | 9–12 hours |
| Teenagers (14–17 years) | 8–10 hours |
| Adults (18–64 years) | 7–9 hours |
| Older adults (65+) | 7–8 hours |
More detail, and how to work out your own number rather than the population average, is in the guide to how much sleep you need.
Guides and calculators
- Sleep cycles explained
- How to sleep better
- How to fall asleep fast
- When you can't sleep
- Sleep hygiene
- Bedtime routine calculator
- Why am I always tired?
- Sleep cycle calculator
- How much sleep do I need?
- Bedtimes by age
- What time should I wake up?
- The best time to sleep
- Build a sleep schedule
- Nap calculator
- Jet lag calculator
- Sleep debt calculator
Sleep stages and tracking
- How much deep sleep?
- REM sleep explained
- What is core sleep?
- How sleep trackers work
- Melatonin in the UK
Is that much sleep enough?
- Is 4 hours enough?
- Is 5 hours enough?
- Is 6 hours enough?
- Is 7 hours enough?
- Is 8 hours enough?
- Is too much sleep bad?
Children's bedtimes
- 1-year-olds
- 2-year-olds
- 3-year-olds
- 4-year-olds
- 5-year-olds
- 6-year-olds
- 7-year-olds
- 8-year-olds
- 9-year-olds
- 10-year-olds
- 11-year-olds
- 12-year-olds
- 13-year-olds
- 14-year-olds
- 15-year-olds
- 16-year-olds
- Teenagers
Common questions
How does a sleep calculator work?
It counts backwards from the time you need to be awake in 90-minute sleep cycles, and adds about 15 minutes for falling asleep. Waking at the end of a cycle rather than in the middle of one means waking from lighter sleep, which is what makes the first half-hour of the morning easier.
What time should I go to bed?
Whatever time gives you 7 to 9 hours before your alarm, plus about 15 minutes to fall asleep. For a 7:00 AM wake-up that is between 9:45 PM and 11:45 PM.
How many hours of sleep do I need?
Adults aged 18 to 64 need 7 to 9 hours. Teenagers need 8 to 10 hours, school-age children 9 to 12, and adults over 65 need 7 to 8.
How long is a sleep cycle?
About 90 minutes on average. The first cycle of the night is usually the shortest at around 70 to 100 minutes, and later cycles run between 90 and 120 minutes. Most people go through four to six cycles a night.
Is it better to sleep 6 hours or 7.5 hours?
Seven and a half hours. Total sleep matters more than landing on a neat number of sleep cycles, so it is never worth cutting sleep short to hit a multiple of 90 minutes.
Does the calculator store my times?
No. All the maths runs in your browser and the time you choose is never sent anywhere.