health calculator
Plan bedtimes and wake times around sleep cycles.
Keep this page saved to quickly find the best bedtime or wake time when your schedule changes.
Suggested bedtime
11:15 PM
Formula
Bedtime = wake time - sleep cycles x 90 minutes - sleep latencyThe calculator works backward from wake time using 90-minute sleep cycles plus time to fall asleep.
Step by step
Example
For a 7:00 AM wake time, five sleep cycles, and 15 minutes to fall asleep, bedtime is about 11:15 PM.
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Summary
Suggested bedtime
11:15 PM
To wake refreshed.
Sleep duration
7.5 hours
Total sleep duration.
Sleep cycles
5 cycles
Completed 90-minute sleep cycles.
Latency buffer
15 min
Estimated time to fall asleep.
D3 visualization
See the ratio of actual sleep duration vs time spent falling asleep (in minutes).
D3 visualization
Compare sleep duration (hours) across different completed 90-minute sleep cycles.
Guide
Healthy human sleep is not a flat state of rest. Instead, it is divided into repeating cycles of light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Each full cycle lasts approximately 90 minutes on average.
Waking up at the end of a completed cycle is associated with feeling alert and refreshed. Conversely, waking up in the middle of a deep sleep phase can trigger sleep inertia, causing grogginess that lasts for hours.
To optimize your sleep, calculate backward or forward from your desired wake time using 90-minute blocks. The calculator automatically adds a 15-minute buffer (sleep latency) to account for the typical time it takes to fall asleep.
For most adults, targeting 5 or 6 complete sleep cycles (7.5 to 9 hours of sleep) is ideal.
Sleep inertia
The temporary state of grogginess experienced when waking abruptly from deep sleep.
Circadian rhythm
Your body's natural 24-hour internal clock regulating sleep and wakefulness.
REM sleep
The active dreaming stage of sleep, crucial for emotional regulation and memory consolidation.
Sleep latency is the time it takes to transition from full wakefulness to sleep. The typical healthy average is between 10 and 20 minutes.
You may have been woken up by an alarm in the middle of a deep sleep phase, or your sleep quality was disrupted by light, noise, or metabolic factors.