Sleep Calculator
Find your ideal bedtime or wake time based on 90-minute sleep cycles. Calculate how many cycles you get and whether you're meeting your sleep needs. Free, instant.
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Disclaimer: Results are for informational purposes only and do not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare professional for personal guidance.
Understanding Sleep Cycles
Sleep is not a single uniform state but a repeating cycle of approximately 90 minutes. Each cycle moves through N1 (light sleep), N2 (consolidated sleep), N3 (deep restorative sleep), and REM sleep (dreaming, memory consolidation). Adults complete 4–6 cycles per night. Waking during N3 or REM produces grogginess (sleep inertia); waking between cycles feels more natural.
How Much Sleep Do You Need?
The National Sleep Foundation's consensus recommendations: adults 18–64: 7–9 hours; older adults 65+: 7–8 hours; teenagers 14–17: 8–10 hours; school-age children 6–13: 9–11 hours. These are population averages — individual needs vary, but consistent sleep below 6 hours is unambiguously associated with health risk regardless of self-reported "feeling fine."
FAQs
How many hours do I need?
Adults: 7–9 hours. Teenagers: 8–10 hours. Older adults: 7–8 hours. Children: 9–11 hours. Below 6 hours consistently carries significant health risks.
What are sleep cycles?
Sleep cycles last ~90 minutes and include light, deep, and REM sleep. Adults complete 4–6 cycles per night. Waking at cycle end feels easier than mid-cycle.
When should I go to sleep?
Count back 7.5h (5 cycles) or 9h (6 cycles) from wake time, add 15 minutes to fall asleep. To wake at 7am: be asleep by 11:15pm or 9:45pm.