# Sleep Calculator: When to Go to Bed and When to Wake Up

Find a bedtime for your wake-up time, or when to set an alarm, based on 90-minute sleep cycles and the AASM's recommended hours of sleep for each age.

Interactive tool: https://lookup.sg/tools/sleep-calculator

## How this works
Sleep runs in cycles of light, deep and REM sleep that last roughly 90 minutes on average. This calculator counts back from your wake-up time (or forward from your bedtime) in whole 90-minute cycles, then adds the time it takes to fall asleep, 15 minutes by default, which you can change.

Options are marked as recommended when the hours of sleep fall in the American Academy of Sleep Medicine's range for that age: 12 to 16 hours a day for babies aged 4 to 12 months, 11 to 14 for ages 1 to 2, and 10 to 13 for ages 3 to 5 (all including naps), 9 to 12 for ages 6 to 12, 8 to 10 for teenagers aged 13 to 18, and 7 hours or more for adults.

Cycle length differs between people and across the night, so the times are a starting point rather than a rule. Keeping the same wake-up time every day, weekends included, matters more than hitting an exact cycle.

## FAQs
### What time should I go to bed if I wake up at 7 am?
Go to bed at 11:15 pm for five 90-minute cycles (7.5 hours of sleep), or at 9:45 pm for six cycles (9 hours), allowing 15 minutes to fall asleep.

### How many hours of sleep do I need?
Adults need 7 hours or more a night. Teenagers aged 13 to 18 need 8 to 10 hours, children aged 6 to 12 need 9 to 12 hours, and children aged 3 to 5 need 10 to 13 hours including naps, according to the American Academy of Sleep Medicine.

### How long is one sleep cycle?
About 90 minutes on average, so a 7.5-hour night is five cycles. Each cycle moves through light sleep, deep sleep and REM sleep, and REM periods get longer towards the morning.

### What time should a 10-year-old sleep for school?
A child aged 6 to 12 needs 9 to 12 hours. For a 6:00 am wake-up for school, that means asleep by 9:00 pm at the latest, so in bed by about 8:45 pm.

## Sources
- [AASM: Recommended amount of sleep for pediatric populations (J Clin Sleep Med 2016)](https://pubmed.ncbi.nlm.nih.gov/27250809/)
- [AASM and SRS: Recommended amount of sleep for a healthy adult (Sleep 2015)](https://pubmed.ncbi.nlm.nih.gov/26039963/)
- [NINDS: Brain basics, understanding sleep](https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep)

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