In this guide
Quick answer: sleep runs in cycles of roughly 90 minutes, and most adults need at least 7 hours a night, which is about 5 cycles. Cycle length varies from person to person.
What is a sleep cycle?
During the night your brain moves through repeating stages of sleep. A full cycle usually lasts about 90 minutes, though it can be somewhat shorter or longer. Most people go through four to six cycles in a night.
The stages of sleep
- Light sleep: the transition into sleep, when you are easy to wake.
- Deep sleep: the most restorative stage, harder to wake from, more common early in the night.
- REM sleep: the stage linked with vivid dreams, more common in the second half of the night.
How many hours do you need?
| Age | Recommended sleep per night |
|---|---|
| 6 to 12 years | 9 to 12 hours |
| 13 to 18 years | 8 to 10 hours |
| 18 to 60 years | 7 or more hours |
| 61 to 64 years | 7 to 9 hours |
| 65 and older | 7 to 8 hours |
These are general recommendations from US health authorities. Individual needs vary.
Why waking at the end of a cycle can feel easier
Being woken from deep sleep can leave you groggy, a feeling called sleep inertia. Aiming to wake between cycles, when sleep is lighter, may help some people feel more alert, but the effect differs from person to person.
Timing your bedtime
Count back from your wake-up time in 90-minute steps and add about 15 minutes to fall asleep. For a 7:00 a.m. alarm, five cycles means going to bed around 11:15 p.m. The sleep calculator does this for you.
Habits that help
- Keep a regular sleep and wake time, including at weekends.
- Limit caffeine in the afternoon and evening.
- Keep the bedroom dark, cool and quiet.
- Avoid bright screens shortly before bed.
When to see a doctor
Trouble sleeping most nights, loud snoring with pauses in breathing, or heavy daytime sleepiness can be signs of a sleep disorder. This guide is general information, not medical advice, so speak to a doctor if you are concerned.
Try the calculators
- Sleep Calculator: Bedtime and wake-up times by sleep cycles
- BMI Calculator: Body mass index and healthy range
General information only, not professional advice. See our editorial policy.