A sleep cycle lasts about 90 minutes, and most adults need about 7 to 9 hours, which is five or six cycles. To pick a bedtime, count back in 90-minute steps from the time you need to wake, and add roughly 15 minutes to fall asleep.
Waking at the end of a cycle, rather than in the middle of deep sleep, often feels easier. The numbers are a guide, because cycle length varies from person to person and from night to night.
What is a sleep cycle?
During the night you move through lighter sleep, deeper sleep and REM (dream) sleep, then start again. One full loop averages about 90 minutes, though it can be shorter or longer for you. Deep sleep tends to dominate the early part of the night, and REM periods get longer towards the morning.
Being woken during deep sleep can leave you groggy, which is sometimes called sleep inertia. Timing your alarm near the end of a cycle may help, but it is no substitute for getting enough sleep overall.
How many hours do you need?
The NHS says most adults need between 6 and 9 hours, and a common rule of thumb is about 7 to 9. In cycle terms:
| Cycles | Time asleep |
|---|---|
| 3 | 4 h 30 min |
| 4 | 6 h |
| 5 | 7 h 30 min |
| 6 | 9 h |
Children and teenagers need more than adults. If you regularly feel tired, or need a lot more or less sleep than the guide suggests, speak to a GP.
How to calculate your bedtime
Use this simple method:
- Choose the time you need to wake up.
- Subtract 90 minutes for each cycle you want, usually five or six.
- Subtract another 15 minutes or so for falling asleep.
For a 7:00 am alarm and five cycles, that is 7 h 30 min of sleep plus 15 minutes to drop off, so you need to be in bed by 11:15 pm. Our Sleep calculator tool gives the same answer, plus the other options:
| Bedtime | Cycles | Sleep |
|---|---|---|
| 9:45 pm | 6 | 9 h |
| 11:15 pm | 5 (best) | 7 h 30 min |
| 12:45 am | 4 | 6 h |
| 2:15 am | 3 | 4 h 30 min |
Working out when to wake up
Going the other way works too. If you are going to bed at 11:00 pm and take 15 minutes to fall asleep, five cycles ends at 6:45 am and six cycles at 8:15 am. Four cycles would wake you at 5:15 am, which is a short night for most adults.
If you set an alarm for a time between cycles, you may not notice much difference. Cycle length shifts, so if you feel better waking ten minutes earlier or later, trust that.
Why the 90-minute figure is only a guide
The 90-minute average hides plenty of variation. Early cycles can be shorter, later ones longer, and age, stress, alcohol and caffeine all change how you move through the stages. Wearable devices that claim to track stages are not medical devices, so use them with caution.
A practical approach is to pick a target of five or six cycles, try it for a week or two, and note how you feel on waking. Adjust the bedtime by 15 or 30 minutes until you find what works for you.
Tips for better sleep
- Keep a regular bedtime and wake time, including at weekends where you can.
- Keep the bedroom cool, dark and quiet.
- Avoid caffeine late in the day. Our guide to How much water should you drink each day? also covers other drinks that count towards your day.
- Wind down without bright screens for a while before bed.
- Avoid heavy meals and alcohol close to bedtime.
- Exercise earlier in the day if late sessions keep you awake. See Running pace and race finish times explained if you are planning a training routine.
Sleep also affects appetite and energy. Our Calories and TDEE: how many calories do you need? guide looks at how much you eat and burn each day.
Note: This is general information, not medical advice. Our tool gives an estimate. If you struggle to sleep for weeks, snore heavily or feel unusually sleepy in the day, see a GP.
Try the calculator
Enter your wake-up time or bedtime into the Sleep calculator calculator to see the best times, including how long you usually take to fall asleep.
Open the free Sleep calculator
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, but it varies between people and through the night.
Is five cycles enough?
Five cycles is 7 hours 30 minutes, which falls within the range of about 7 to 9 hours most adults need. Some people feel better with six.
Do I need to wake at the end of a cycle?
No. It can help you feel less groggy, but total sleep matters more than exact timing.
What if I fall asleep faster or slower than 15 minutes?
Adjust the figure in the calculator. If you regularly take much longer than 30 minutes, talk to a GP.