How the wake-up calculator works
Through the night you move through repeating sleep cycles of light, deep and REM sleep, each lasting about 90 minutes on average. Waking at the end of a cycle, when sleep is lighter, usually feels easier than being pulled out of deep sleep.
The calculator starts at your bedtime, adds the time you usually take to fall asleep, then adds whole cycles: 6 cycles (9 hours), 5 cycles (7.5 hours) or 4 cycles (6 hours). If you tap “I’m going to sleep now”, it reads the current time from your device and uses that as your bedtime. Nothing is sent anywhere.
Each result shows the alarm time in 12-hour and 24-hour format, and whether it falls on the same day or the next day.
Worked example: bed at 11:00 PM
You get into bed at 11:00 PM and usually fall asleep in about 15 minutes, so your first cycle starts at 11:15 PM.
| Sleep | Wake up | 24-hour | Day |
|---|---|---|---|
| 9 h · 6 cycles | 8:15 AM | 08:15 | Next day |
| 7.5 h · 5 cycles | 6:45 AM | 06:45 | Next day |
| 6 h · 4 cycles | 5:15 AM | 05:15 | Next day |
If it takes you 30 minutes to fall asleep instead, every wake-up time moves 15 minutes later.
Choosing a wake-up time
Adults are advised to get at least 7 hours of sleep on a regular basis, so the 9-hour and 7.5-hour options are marked recommended. The 6-hour option is for nights when you can’t fit in more.
If none of the times suit your morning, it usually works better to move your bedtime than to cut a cycle short. The bedtime calculator works backwards from a fixed alarm.
When to seek help
Talk to a doctor or a sleep specialist if you:
- regularly take longer than 30 minutes to fall asleep, or wake in the night and can’t get back to sleep;
- snore loudly, or someone notices you gasp or stop breathing while asleep;
- feel very sleepy during the day, especially while driving or working, despite enough time in bed;
- have had trouble sleeping for several weeks and it’s affecting your mood, health or daily life.
Frequently asked questions
What time should I wake up if I go to bed at 11 PM?
Allowing 15 minutes to fall asleep, try 6:45 AM for 7.5 hours of sleep or 8:15 AM for 9 hours. 5:15 AM gives 6 hours, which is short for most adults.
How does “I’m going to sleep now” work?
When you tap it, the page reads the current time from your device clock, sets it as your bedtime and updates the results. It happens entirely in your browser.
Why does it say “next day”?
Any wake-up time after midnight falls on the following calendar day. The label makes it clear which day your alarm needs to be set for, which helps with night shifts and late bedtimes.
What if I wake up before my alarm?
If you wake near one of these times feeling rested, it’s often fine to get up. Cycle lengths vary from person to person and across the night, so treat the times as a guide.
Related calculators
Bedtime calculator
Know when you need to wake up? Find the bedtimes that let you wake between sleep cycles.
Nap calculator
Plan a 10-, 20- or 90-minute nap and see when to set your alarm.
Sleep needs by age
See the recommended hours of sleep for any age, from newborns to older adults.
Sleep debt calculator
Add up the last seven nights and see how far you are from your sleep target.
Sources
- National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep.
- National Heart, Lung, and Blood Institute. How Sleep Works.
- Centers for Disease Control and Prevention. About Sleep.
- Watson NF, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, 2015;11(6):591–592. doi:10.5664/jcsm.4758.