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About the sleep calculator
Sleep comes in cycles of about 90 minutes: light sleep, deep sleep and dream sleep. If your alarm wakes you in the middle of deep sleep, you feel heavy and tired. If it wakes you at the end of a cycle, it is much easier to get up.
This calculator counts the cycles for you. Choose one of three ways:
- I want to wake up at — it shows the times to go to bed
- I go to bed at — it shows the times to set your alarm
- Sleep now — it uses the current time and shows when to wake up
The result lists 6, 5, 4 and 3 cycles (9, 7.5, 6 and 4.5 hours of sleep). Five or six cycles suit most adults, who need about 7 to 9 hours a night.
How to use it
- Pick I want to wake up at, I go to bed at or Sleep now
- Choose the time
- Read the list — the best choice, 5 cycles (7.5 hours), is on top
- Open More options to change the minutes to fall asleep (15 is the average) and the length of the sleep cycle (90 minutes)
Bedtimes for a wake-up time
With 15 minutes to fall asleep and 90-minute cycles:
| Wake up at | 6 cycles (9 h) | 5 cycles (7.5 h) | 4 cycles (6 h) | 3 cycles (4.5 h) |
|---|---|---|---|---|
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM | 1:15 AM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM | 1:45 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM | 2:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM | 3:15 AM |
And if you go to bed at 11:00 PM, set your alarm for 5:15 AM (4 cycles), 6:45 AM (5 cycles) or 8:15 AM (6 cycles).
How much sleep do I need?
| Age | Hours a night |
|---|---|
| Teenagers (14–17) | 8–10 |
| Adults (18–64) | 7–9 |
| Older adults (65+) | 7–8 |
Some people do well on a little less or need a little more. If you feel awake all day, your amount is fine.
Tips for better sleep
- Go to bed and wake up at the same time every day, also on weekends
- Keep the room dark, cool and quiet
- Put screens away an hour before bed
- No caffeine after the early afternoon
- Do not eat a big meal or drink alcohol close to bedtime
Frequently asked questions
How does the sleep calculator work?
It counts 90-minute sleep cycles back from your wake-up time (or forward from your bedtime) and adds the time you need to fall asleep.
Is a sleep cycle always 90 minutes?
No, it is an average. It can be 80 to 100 minutes and changes during the night. You can change it under More options.
How many cycles should I sleep?
Five cycles (7.5 hours) or six (9 hours) for most adults. Four cycles (6 hours) is the least that most people can keep up for a few days.
What about naps?
A short nap of 20 minutes gives a boost without deep sleep. A full cycle of 90 minutes also works. Avoid 30–60 minutes — you wake in deep sleep.
Why do I wake up tired even after 8 hours?
Stress, an irregular schedule, alcohol, a noisy room or a medical problem like sleep apnea can all spoil sleep. If it lasts, ask a doctor.
Is this medical advice?
No. It is a general guide. If you have sleep problems, talk to a doctor.
Good to know
- Your settings are saved only in this browser
- Times are shown in the format of your language
- Nothing you type is sent anywhere
Related tools
- Alarm Clock — set the time you found
- Countdown to Date — count down to the weekend
- World Clock — see the time in another city
- Stopwatch — time a nap
- Water Intake Calculator — drink enough during the day
