Sleep Calculator

Adults (18–64): 7–9 hours per night. Older adults (65+): 7–8 hours. Teenagers (14–17): 8–10 hours. School-age children (6–13): 9–11 hours. These are average needs — some individuals genuinely function well on 6 or need 10 hours.

A sleep cycle lasts approximately 90 minutes and includes light sleep (N1, N2), deep sleep (N3/slow-wave sleep), and REM sleep. Most people complete 4–6 cycles per night. Waking at the end of a cycle (vs. mid-cycle) dramatically reduces grogginess.

Sleep inertia — grogginess upon waking — is worst when you wake during deep sleep (N3 stage). Waking at the end of a 90-minute cycle, when sleep is lightest, minimizes this. This is the basis of sleep cycle-based alarm timing.

REM (Rapid Eye Movement) sleep is when most dreaming occurs. It is critical for memory consolidation, emotional processing, and creativity. REM periods lengthen later in the night — a major reason why cutting sleep short (especially skipping the last 1–2 hours) significantly impairs cognitive function.

Blue light from screens suppresses melatonin production, delaying sleep onset by 1–3 hours. Avoiding screens 1–2 hours before bed, using night mode, or wearing blue-light glasses can help. The stimulating content of social media and news also increases alertness regardless of light.