Sleep Calculator
Find a bedtime from your wake-up time, or a wake-up time from your bedtime, using 90-minute sleep cycles.
Results
| Go to bed at | Sleep cycles | Sleep time |
|---|
Quick Answer
Count back from your wake-up time in 90-minute sleep cycles, then allow time to fall asleep. To wake at 7:00 AM after 5 cycles (7.5 hours), with 15 minutes to fall asleep, go to bed at 11:15 PM. Adults generally need 7 or more hours of sleep.
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Table of Contents
How This Sleep Calculator Works
During the night, your body moves through repeating sleep cycles. This calculator uses a 90-minute average to suggest times that line up with the end of a cycle. It also adds the time you usually need to fall asleep.
Quick explanation: Bedtime = wake-up time − (cycles × 90 minutes) − time to fall asleep.
- Bedtime mode: enter when you need to wake up.
- Wake-up mode: enter when you plan to go to bed.
- Highlighted row: 5 cycles, or 7.5 hours of sleep.
Core Formulas
- Sleep time: cycles × 90 minutes
- Bedtime: wake-up time − sleep time − minutes to fall asleep
- Wake-up time: bedtime + minutes to fall asleep + sleep time
Research describes cycles of roughly 90 to 110 minutes, and some sources say up to 120. The 90-minute figure is an average, so treat these times as a guide and not an exact rule.
Worked Example
You go to bed at 10:30 PM and take 15 minutes to fall asleep.
- Asleep at 10:45 PM
- 5 cycles = 7.5 hours, so wake at 6:15 AM
- 6 cycles = 9 hours, so wake at 7:45 AM
Getting Better Sleep
- Keep a routine: going to bed and waking at similar times helps.
- Think about total sleep: the number of hours matters more than hitting an exact cycle.
- Age matters: children and teens need more sleep than adults.
- Get help if needed: speak to a doctor if you often feel tired or have trouble sleeping.
Frequently Asked Questions
It counts in sleep cycles of about 90 minutes from the time you enter, then allows for the time it takes you to fall asleep.
For 5 cycles, go to bed at about 11:15 PM. For 6 cycles, go to bed at about 9:45 PM. Both include 15 minutes to fall asleep.
The CDC recommends at least 7 hours a night for adults. Older adults aged 65 and over are advised to get 7 to 8 hours.
About 90 minutes on average, though research shows roughly 90 to 110 minutes or longer. Cycles also change through the night.
Many people find it helps, but the evidence is limited. Getting enough total sleep on a regular schedule matters more.
References & Sources
| Source | Used For | Link |
|---|---|---|
| CDC, About Sleep | Recommended hours of sleep by age. | https://www.cdc.gov/sleep/about/index.html |
| NCBI StatPearls, Physiology, Sleep Stages | Sleep cycle length and stages. | https://www.ncbi.nlm.nih.gov/books/NBK526132/ |
| AASM and SRS consensus statement (PMC) | Recommended sleep for healthy adults. | https://pmc.ncbi.nlm.nih.gov/articles/PMC4434546/ |