Productive ToolboxSleep Calculator
Find the best time to go to bed or wake up, timed to 90-minute sleep cycles, so you wake up between cycles rather than in deep sleep.
Go to bed at one of these times
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How Sleep Cycles Work
Through the night you pass through repeating cycles of light sleep, deep (slow-wave) sleep and REM sleep, each lasting roughly 90 minutes. Most adults need four to six cycles. Timing your alarm for the end of a cycle, when sleep is lightest, can make waking up easier.
Bedtime = Wake-up time − (cycles × 90 min) − time to fall asleep
Wake-up time = Bedtime + time to fall asleep + cycles × 90 min
Example: to wake at 6:30 AM after five cycles, with 15 minutes to fall asleep, go to bed at 10:45 PM.
How Much Sleep Do You Need?
| Age group | Hours per 24 hours |
|---|---|
| Infants 4–12 months | 12–16 (including naps) |
| Children 1–2 years | 11–14 (including naps) |
| Children 3–5 years | 10–13 (including naps) |
| Children 6–12 years | 9–12 |
| Teenagers 13–18 years | 8–10 |
| Adults 18 and over | 7 or more (7–9) |
American Academy of Sleep Medicine consensus recommendations (2016).
How to Use the Sleep Calculator
- 1Choose what you know: Pick I want to wake up at to get bedtimes, I'm going to bed at to get alarm times, or I'm going to bed now.
- 2Enter the time: Set your wake-up time or bedtime; times use your device's 12- or 24-hour format.
- 3Adjust the details: Set how long you usually take to fall asleep (15 minutes is typical) and, if you know it, your sleep cycle length.
- 4Pick a time: Choose one of the suggested times; 5 or 6 cycles give 7.5 to 9 hours of sleep, the range recommended for adults.
Frequently Asked Questions
How does the sleep calculator work?
Sleep runs in cycles of light, deep and REM sleep that last about 90 minutes. The calculator counts back (or forward) whole cycles from your wake-up time or bedtime and adds the time it takes to fall asleep. To wake at 7:00 AM after six cycles and 15 minutes to fall asleep, go to bed at 9:45 PM.
Why wake up at the end of a sleep cycle?
Waking from deep sleep often leaves you groggy, a state called sleep inertia. Waking in light sleep near the end of a cycle usually feels easier. Cycle length varies from person to person and through the night, so treat the times as a guide.
How much sleep do adults need?
At least 7 hours a night, and 7–9 hours for most adults, according to the American Academy of Sleep Medicine and the Sleep Research Society. Five cycles is 7.5 hours and six cycles is 9 hours.
How long should it take to fall asleep?
Around 10–20 minutes for most healthy adults. Falling asleep within a couple of minutes every night can be a sign of sleep deprivation, while regularly taking longer than 30 minutes may point to insomnia.
Is a sleep cycle always 90 minutes?
No. Cycles typically last 70–120 minutes, with more deep sleep early in the night and more REM sleep toward morning. If you know your own pattern from a sleep tracker, change the cycle length.
What if I often wake up tired?
Keep a regular sleep and wake time, including weekends, limit caffeine after midday and screens before bed, and keep your bedroom dark and cool. See a doctor if you snore loudly, stop breathing during sleep or feel sleepy during the day despite enough sleep.
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