Sleep Calculator
Sleep cycles last ~90 minutes. Waking between cycles feels most natural.
Sleep occurs in cycles of approximately 90 minutes, each consisting of several stages including light sleep, deep sleep (slow-wave sleep), and REM sleep. Waking up at the end of a complete cycle — rather than in the middle of deep sleep — significantly reduces sleep inertia (that groggy feeling). The calculator adds 14 minutes (average time to fall asleep) to the sleep time to give you accurate bedtimes or wake-up times aligned with natural cycle boundaries.
Frequently Asked Questions
How long is one sleep cycle?
A complete sleep cycle lasts approximately 90 minutes and consists of: N1 (light sleep, ~5 min), N2 (light sleep, ~25 min), N3 (deep/slow-wave sleep, ~30 min), and REM (rapid eye movement, ~30 min). The proportion of REM sleep increases in later cycles, while deep sleep dominates early in the night.
Why does the calculator add 14 minutes?
The average person takes about 14 minutes to fall asleep after lying down. This is added to the recommended sleep duration so that your bedtime recommendation accounts for the time it actually takes to transition from wakefulness to the first sleep stage.
How many sleep cycles do I need?
Adults need 7–9 hours of sleep per night, which corresponds to 5–6 full cycles (450–540 minutes). 4 cycles (6 hours) is the minimum many function on, but research consistently shows that 5–6 cycles (7.5–9 hours) is optimal for cognitive performance, mood, and physical health.
What if I can't fall asleep exactly at the suggested time?
The 14-minute estimate is an average. If you know it takes you longer (e.g., 30 minutes), mentally adjust the bedtime earlier by the difference. The key goal is to wake up after a complete cycle — even 5–10 minutes late means you're in a new cycle, and waking mid-cycle can still cause grogginess.