Sleep Calculator: Best Bedtime and Wake-Up Time
Find when to go to bed or wake up so you finish a full 90-minute sleep cycle. Allows for the time it takes to fall asleep and shows recommended sleep by age. Runs in your browser; nothing is sent.
Go to bed at one of these times
- 21:45the day before6 cycles, 9 hours of sleepRecommended
- 23:15the day before5 cycles, 7 hours 30 minutes of sleepRecommended
- 00:454 cycles, 6 hours of sleep
| Age group | Ages | Sleep per day |
|---|---|---|
| Newborns | 0 to 3 months | 14 to 17 hours |
| Infants | 4 to 11 months | 12 to 15 hours |
| Toddlers | 1 to 2 years | 11 to 14 hours |
| Preschoolers | 3 to 5 years | 10 to 13 hours |
| School-age children | 6 to 13 years | 9 to 11 hours |
| Teenagers | 14 to 17 years | 8 to 10 hours |
| Young adults | 18 to 25 years | 7 to 9 hours |
| Adults | 26 to 64 years | 7 to 9 hours |
| Older adults | 65 years and over | 7 to 8 hours |
About the Sleep Calculator
The Sleep Calculator suggests when to go to bed or when to set your alarm so that you wake at the end of a sleep cycle rather than in the middle of one. Choose Wake up at to get bedtimes for a fixed alarm, Go to bed at to get wake-up times for a planned bedtime, or Go to bed now to get wake-up times starting from the current time. Each suggestion shows the number of cycles, the hours of sleep it gives and whether it meets the adult recommendation.
Times are shown as 24-hour clock times and wrap correctly across midnight, so a bedtime of 23:15 for a 07:00 alarm is marked as the day before.
This is an estimate, not medical advice. Sleep cycles differ between people and between nights, so the suggested times are a starting point. Persistent tiredness, loud snoring or trouble falling asleep are worth discussing with a doctor.
How it works
Sleep cycles
During the night the brain moves through repeating cycles of light sleep, deep sleep and REM sleep. One cycle lasts about 90 minutes on average, though it can range from roughly 80 to 120 minutes. Waking at the end of a cycle, when sleep is lightest, tends to feel easier than being woken from deep sleep.
Time to fall asleep
Most people take 10 to 20 minutes to fall asleep, so the calculator adds 15 minutes by default. Change it to anything from 0 to 60 minutes to match how long you usually lie awake.
Steps
- Choose whether you know your wake-up time, your bedtime, or want to go to bed now.
- Enter the time and, if needed, how long you take to fall asleep.
- Pick one of the suggested times. Five or six cycles are recommended for adults.
The formula
The calculator uses 4, 5 and 6 cycles, which give 6, 7.5 and 9 hours of sleep. For a 07:00 alarm and 15 minutes to fall asleep, the bedtimes are 21:45 and 23:15 the day before, and 00:45.
How much sleep you need
The American Academy of Sleep Medicine and the Sleep Research Society agreed in 2015 that adults should sleep 7 or more hours a night on a regular basis, which is why 5 and 6 cycles are marked recommended and 4 cycles is not. The National Sleep Foundation's 2015 ranges, shown in the table on the page, recommend 14 to 17 hours for newborns, 9 to 11 hours for school-age children, 8 to 10 hours for teenagers, 7 to 9 hours for adults and 7 to 8 hours from age 65.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device. Nothing is saved.
Related tools
Add up hours and minutes with the Time Calculator, or count the hours worked in a shift with the Hours Calculator.
Sources
- Watson NF et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the AASM and SRS. J Clin Sleep Med 2015;11(6):591-592; Sleep 2015;38(6):843-844.
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health 2015;1(1):40-43.
- Carskadon MA, Dement WC. Normal human sleep: an overview. In: Kryger MH, Roth T, Dement WC, eds. Principles and Practice of Sleep Medicine.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party libraries. They follow the 90-minute sleep cycle described in the sleep medicine literature above, the AASM and SRS adult recommendation and the National Sleep Foundation age ranges.
Frequently asked questions
Why does the calculator use 90-minute cycles?
Sleep runs in repeating cycles of light, deep and REM sleep that last about 90 minutes on average. Waking at the end of a cycle, when sleep is lightest, usually feels easier than waking from deep sleep. Real cycles vary from about 80 to 120 minutes, so the suggested times are a guide.
How many hours of sleep do adults need?
The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours a night for adults. That is why 5 cycles (7 hours 30 minutes) and 6 cycles (9 hours) are marked recommended, and 4 cycles (6 hours) is not.
What is the time to fall asleep setting?
It is the time between getting into bed and falling asleep. Most people take 10 to 20 minutes, so the default is 15. The calculator adds it to every suggestion, so change it if you usually fall asleep faster or more slowly.
How much sleep do children and teenagers need?
The National Sleep Foundation's 2015 recommendations are 14 to 17 hours for newborns, 12 to 15 for infants, 11 to 14 for toddlers, 10 to 13 for preschoolers, 9 to 11 for school-age children and 8 to 10 for teenagers. The full table is shown on the page.
Is my time sent anywhere?
No. The times are calculated in your browser, nothing is sent to a server, and nothing is saved, so the page works the same offline once it has loaded.