Sleep Calculator
Find the best time to go to bed or wake up, based on 90-minute sleep cycles, so you wake between cycles and feel refreshed.
Adults need 7 to 9 hours of sleep. Teenagers need 8 to 10 hours, and children need more.
How the sleep calculator works
During the night you move through repeating sleep cycles. Each one passes through light sleep, deep sleep and dream (REM) sleep, and lasts about 90 minutes on average. Waking up at the end of a cycle, when sleep is lightest, usually feels much easier than being woken from deep sleep in the middle of one.
The calculator counts back (or forward) in whole cycles from the time you choose, and adds the time it takes you to fall asleep, 15 minutes by default.
How to use it
- I want to wake up at: enter your alarm time to see when to go to bed for 3 to 6 full cycles.
- I’m going to bed at: it starts at the current time, so if you are going to bed now you can see the best times to set your alarm straight away.
The suggestion marked Best gives 5 cycles, about 7.5 hours of sleep, which suits most adults. Choose 6 cycles if you often feel tired during the day.
How much sleep do you need?
- Adults (18 to 64): 7 to 9 hours
- Older adults (65+): 7 to 8 hours
- Teenagers (14 to 17): 8 to 10 hours
- Children (6 to 13): 9 to 11 hours
Tips for better sleep
- Go to bed and get up at the same time every day, including weekends.
- Keep your bedroom dark, quiet and cool.
- Avoid caffeine in the afternoon and large meals late at night.
- Put screens away for 30 to 60 minutes before bed.
Cycle length varies from person to person. If you still wake up groggy, try adjusting the cycle length a little. If you often struggle to sleep or feel exhausted, talk to a doctor.
Sleep Calculator FAQs
Answers about sleep cycles and bedtimes.
What time should I go to bed to wake up at 7 AM?+
For 5 sleep cycles (7.5 hours) plus 15 minutes to fall asleep, go to bed at 11:15 PM. For 6 cycles (9 hours), go to bed at 9:45 PM.
How long is a sleep cycle?+
About 90 minutes on average, though it can range from about 80 to 110 minutes and varies through the night and between people.
Why do I feel groggy even after a long sleep?+
Waking up during deep sleep causes grogginess, called sleep inertia. Timing your alarm to the end of a cycle can help.
Is 6 hours of sleep enough?+
Not for most adults. Health guidelines recommend 7 to 9 hours. Regularly sleeping less is linked to tiredness and long-term health problems.
Does the calculator use my location or time zone?+
No. It works with the times you enter and runs entirely in your browser.
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