Sleep Calculator

Adults need 7–9 hours of sleep per night. Teenagers need 8–10 hours and school-age children need 9–12 hours. Sleep needs vary by individual, but consistently getting less than 7 hours is associated with health risks.

Sleep cycles last approximately 90 minutes and include light sleep, deep sleep and REM (rapid eye movement) sleep. Waking up at the end of a complete sleep cycle — rather than mid-cycle — helps you feel more refreshed.

If you need to wake up at a specific time, count back in 90-minute sleep cycles plus 15 minutes to fall asleep. For a 6am wake-up with 5 cycles (7.5 hours): go to sleep at 10:15pm.

Waking mid-cycle causes sleep inertia — that groggy, disoriented feeling. Our calculator shows bedtimes that align with complete 90-minute cycles so you wake at the lightest sleep stage feeling more refreshed.

REM (Rapid Eye Movement) sleep is the stage where most dreaming occurs. It is essential for memory consolidation, emotional processing and creativity. REM sleep becomes longer in later cycles, which is why the last 1–2 hours of sleep are particularly valuable.