😴 Sleep Cycle Calculator
Find optimal sleep or wake times based on 90-minute cycles, track sleep debt, and learn about sleep stages.
Sleep Debt Tracker
Enter your sleep for the past 7 nights to calculate cumulative sleep debt.
What Happens During Each Sleep Cycle
Transition from wakefulness. Muscle twitches (hypnic jerks) common. Easily awakened. Brain produces theta waves.
Heart rate slows, body temperature drops. Sleep spindles and K-complexes appear. Memory consolidation begins.
Slow-wave sleep. Most restorative stage — tissue repair, immune function, hormone release. Hardest to wake from.
Rapid eye movement. Vivid dreams occur. Critical for emotional processing, learning, and creativity. Amount increases toward morning.
About Sleep Cycles
A complete sleep cycle lasts approximately 90 minutes and progresses through NREM 1 → NREM 2 → NREM 3 → REM stages. Adults need 4–6 complete cycles per night (6–9 hours). Waking between cycles — rather than mid-cycle — helps you feel more refreshed.
The calculator adds 14 minutes as a typical sleep onset latency (time to fall asleep). If you tend to fall asleep faster or slower, adjust your bedtime accordingly.