What this tool does
Generate possible bedtimes or wake times from an anchor time, estimated time to fall asleep and a user-selected sleep-cycle length.
How to use it
- Choose whether the entered anchor is the time to wake or the time to go to bed.
- Enter the anchor time, expected minutes to fall asleep and a cycle length from 60 to 120 minutes.
- Compare the 4-, 5- and 6-cycle suggestions while still prioritising adequate total sleep and a consistent routine.
Formula and method
For a wake-time anchor, suggested bedtime = anchor − sleep latency − cycle count×cycle minutes. For a bedtime anchor, suggested wake time = anchor + latency + cycle count×cycle minutes. Times wrap across midnight. The default 90 minutes is adjustable; NHLBI describes real cycles as commonly restarting every 80–100 minutes.
Worked example
With a 07:00 wake time, 15-minute sleep latency and 90-minute cycles, the 4-, 5- and 6-cycle bedtimes are 00:45, 23:15 and 21:45. Their calculated sleep portions are 6, 7.5 and 9 hours.
Common uses
- Comparing several bedtime options
- Planning around an early wake time
- Seeing how sleep latency or cycle assumptions shift the clock
Limitations
People do not complete identical cycles on a fixed timer, and normal cycles vary across a night. A suggested boundary does not guarantee easier waking or good-quality sleep. Age, sleep debt, schedules, health and sleep disorders matter. Adults generally need at least 7 hours, and persistent insomnia, snoring or daytime sleepiness deserves clinical advice.
FAQ
Will waking between calculated cycles make me refreshed?
Not reliably. The times are planning scenarios; real sleep stages cannot be identified from clock arithmetic without measurement.
Why can I change the 90-minute cycle?
NHLBI notes that cycles commonly restart every 80–100 minutes, so 90 is a convenient default rather than a universal biological constant.