Sleep Cycle Calculator
Suggest bedtimes from a wake time, or wake times from a bedtime, using repeating cycle blocks (default 90 minutes) plus a fall-asleep buffer (default 14 minutes). Shows 6, 5, 4, and 3 cycle options. Informational sketch, not a medical sleep study.
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How to use the sleep cycle calculator
- Choose whether you start from bedtime or from wake time.
- Enter the matching clock time as HH:MM (24-hour).
- Keep or adjust the fall-asleep buffer and cycle length.
- Read the 6, 5, 4, and 3 cycle suggestions.
- Treat the list as a schedule sketch, not a diagnosis. Nothing is uploaded.
Sleep cycle schedule sketch
Clock arithmetic with N × cycle + buffer
| Default cycle | 90 minutes |
|---|---|
| Default buffer | 14 minutes to fall asleep |
| From bedtime | wake = bed + buffer + N × cycle |
| From wake | bed = wake - buffer - N × cycle |
| N values | 6, 5, 4, and 3 cycles |
| Advice | Informational. Not a sleep disorder test. |
What sleep cycle timing sketches
Popular planners assume sleep arrives in repeating blocks near 90 minutes and that waking near a block boundary feels easier. This page applies that idea with simple clock math. Real sleep architecture is more complex than fixed blocks.
How bed and wake times are built
When calculating wake times: wake = bedtime + fallAsleep + N × cycleMinutes for N in 6,5,4,3. When calculating bedtimes: bedtime = wakeTime - fallAsleep - N × cycleMinutes. Times wrap across midnight in 24-hour HH:MM format.
Clock tools related to sleep planning
Entities include cycle length, fall-asleep buffer, and suggested clock times. Generic duration math lives on time duration. Age from birthdates sits on age.
Use cases
Picking a bedtime that lands near a target wake-up. Comparing 5-cycle and 6-cycle nights for the same alarm. Teaching modular time arithmetic. Not treatment for insomnia or apnea.
Default numbers
Bedtime 23:00 with 14-minute buffer and 90-minute cycles: sleep onset ~23:14. Six cycles add 540 minutes, so wake ≈ 08:14. Five cycles wake ≈ 06:44.
Limits
Chronotype, caffeine, shift work, and clinical sleep disorders are not modeled. Informational only. See the disclaimer. CZNull does not receive schedule times.