Sleep Cycle Calculator
Back-calculate three bedtime options from a target wake time using 4, 5, or 6×90-minute cycles plus sleep-onset time.
How to use
- Choose a target wake time in 24-hour format.
- Enter 0–120 minutes to fall asleep and calculate the 4/5/6-cycle bedtimes.
Capabilities and scope
The runner uses 90 minutes for convenience even though real sleep cycles are not fixed at exactly 90 minutes.
How it works
bedtime=wake−cycles×90min−sleepOnset, wrapped on a 24-hour clock.
Example
For 07:00 wake, 15-minute onset, and six cycles, the computed bedtime is about 21:45.
Interpretation
The runner presents only four, five, and six-cycle options.
Useful for
- See several bedtime candidates from a fixed wake time
- Include estimated sleep-onset time in a simple schedule
Before you use it
- NHLBI describes typical cycles as about 80–100 minutes and variable through the night, so this is not precise sleep-stage prediction.
Edge cases
- Sleep-onset input is limited to 0–120 minutes.
Standards and references
Frequently asked questions
Will waking after a 90-minute multiple always feel better?
No. Cycle length varies between people and across the night, and timing alone cannot guarantee sleep quality.