How many hours of sleep do adults need?
Most adults need 7 to 9 hours a night, according to sleep medicine guidance. Individual needs vary, and a schedule that leaves you tired during the day suggests you need more.
Sleep Calculator
Choose a wake-up time or a bedtime and see the times that line up with complete 90-minute sleep cycles.
Runs in your browser — nothing is uploaded
About the Sleep Calculator
Sleep moves through cycles of about 90 minutes, from light sleep to deep sleep and dreaming. Waking near the end of a cycle, when you are in lighter sleep, often leaves you feeling more rested than being woken in the middle of a deep phase.
Most people take around 15 minutes to fall asleep, which the calculator includes. The times it shows are based on four to six complete cycles, which is roughly 6 to 9 hours. Adults generally need seven or more hours, so choose the option that fits your schedule.
FAQ
Sleep Calculator — frequently asked
Are sleep cycles exactly 90 minutes?
The average is about 90 minutes but it varies between people and across the night. The calculator gives a practical guide rather than an exact prediction.
Why add 15 minutes to fall asleep?
It takes most people around 10 to 20 minutes to drift off. Adding 15 minutes makes the bedtimes more realistic, so you are not counting time you have not yet slept.
Can a sleep calculator fix insomnia?
No. If you regularly take more than 30 minutes to fall asleep or wake often, consider cognitive behavioural therapy for insomnia (CBT-I) or speak with a clinician.
Does caffeine affect these times?
Yes. Caffeine has a half-life of several hours, so an afternoon coffee can keep you awake at bedtime. Many sleep experts suggest avoiding caffeine for about eight hours before bed.
Is my schedule stored?
No. The times are calculated in your browser and nothing is saved.
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