Bedtime 23:00, 6 cycles
Input Bedtime 23:00, 15 minutes to fall asleep.
Result 4 cycles 05:15, 5 cycles 06:45, 6 cycles 08:15, 7 cycles 09:45.
Sleep Cycle Calculator
Everyday LifePick a bedtime or a wake-up time and see the natural wake times after 4, 5, 6 and 7 sleep cycles.
Your inputs
Result
6 cycles (9 h)
—
- 4 cycles (6 h) —
- 5 cycles (7.5 h) —
- 7 cycles (10.5 h) —
Change any input and the result updates instantly.
Formula and rules
- One cycle is about 90 minutes of light, deep and REM sleep
- Time = bedtime + minutes to fall asleep + cycles × 90 minutes
- For a fixed wake-up time: bedtime = wake-up time − minutes to fall asleep − cycles × 90 minutes
- Times are shown on a 24-hour clock and roll over past midnight
Worked examples
Wake at 07:00, which bedtime?
Input Wake-up time 07:00, 15 minutes to fall asleep.
Result For 6 cycles go to bed at 21:45; 5 cycles gives 23:15 and 4 cycles means 00:45.
A late bedtime of 00:30
Input Bedtime 00:30, 20 minutes to fall asleep.
Result 6 cycles puts the alarm at 09:50, 5 cycles at 08:20 and 4 cycles at 06:50.
FAQ
Why is a sleep cycle 90 minutes?
A full cycle through light sleep, deep sleep and REM sleep lasts about 90 minutes in most adults, though individual cycles range from roughly 70 to 120 minutes. Waking at the end of a cycle usually feels easier than waking in the middle of deep sleep.
Why add time to fall asleep?
The 90-minute clock starts when you are asleep, not when you get into bed. Most people need 10 to 20 minutes to fall asleep, so leaving it out would set the alarm too early.
Is 4 cycles enough sleep?
Four cycles is about 6 hours, which is below the 7 to 9 hours most adults need. Use 5 to 6 cycles as the default and treat 4 cycles as an occasional short night, not a habit.
Disclaimer: This estimate uses a typical 90-minute sleep cycle and is a scheduling aid only, not medical advice. If you have long-term insomnia, excessive daytime sleepiness, or snoring with pauses in breathing, see a doctor.