Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles, allowing 15 minutes to fall asleep.
About Sleep Calculator
This sleep calculator suggests the best bedtime or wake-up time using 90-minute sleep cycles. Enter the time you need to wake up and it lists bedtimes that let you finish a full cycle, or enter when you plan to go to bed, or tap Sleep now, to see good wake-up times. It allows about 15 minutes to fall asleep.
Waking at the end of a sleep cycle rather than in the middle of deep sleep can help you feel less groggy. Adults usually do best with five or six cycles a night. The calculator is free, works on any phone or computer and needs no sign-up.
How to use Sleep Calculator
- Choose whether you know your wake-up time or your bedtime.
- Enter the time (or tap “Sleep now”).
- Pick one of the suggested times — 5 or 6 cycles is ideal for adults.
Frequently asked questions
Why 90-minute cycles?
Sleep moves through light, deep and REM stages in cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in deep sleep, usually feels less groggy.
How much sleep do adults need?
7–9 hours for adults (18–64) and 7–8 hours for over-65s, according to the US National Sleep Foundation. That is about 5–6 cycles.
Why add 15 minutes?
Most people take 10–20 minutes to fall asleep. The calculator adds 15 minutes; change it if you usually fall asleep faster or slower.
What time should I sleep to wake up at 6 am?
For five or six full cycles, aim to fall asleep around 10:30 pm or 9 pm; the calculator adds 15 minutes for falling asleep and shows the exact bedtimes.
What are the stages of a sleep cycle?
Each cycle moves through light sleep, deep sleep and REM (dreaming) sleep, and lasts roughly 90 minutes.
Is it better to sleep 6 or 7 hours?
Six hours equals four cycles and 7.5 hours equals five. Most adults need seven or more hours for good health.
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