Sleep Calculator

A sleep cycle lasts approximately 90 minutes and consists of four stages: three stages of non-REM sleep (light to deep sleep) and one stage of REM (Rapid Eye Movement) sleep where dreaming occurs. A full night typically includes 4-6 cycles.

Waking up mid-cycle, especially during deep sleep, causes sleep inertia - the groggy, disoriented feeling that can last for hours. Waking at the end of a complete cycle, when sleep is lightest, makes it much easier to feel alert.

The National Sleep Foundation recommends 7-9 hours for adults aged 18-64, and 7-8 hours for adults 65+. This corresponds to approximately 5-6 sleep cycles. Individual needs vary.

Sleep debt is the cumulative effect of not getting enough sleep. It cannot be fully repaid in one long sleep session. Consistently getting adequate sleep is more beneficial than alternating between sleep deprivation and oversleeping.

Key factors include sleep schedule consistency (same bedtime/wake time), sleep environment (dark, cool, quiet), avoiding screens before bed, limiting caffeine after 2 PM, regular exercise, and managing stress.

Quality sleep supports memory consolidation, hormone regulation (including growth hormone and cortisol), immune function, cardiovascular health, weight management, and mental health. Poor sleep is linked to increased risk of obesity, diabetes, and heart disease.