Sleep Calculator
Waking up mid-sleep-cycle leaves you groggy and tired even after 8 hours. This calculator times your sleep in 90-minute cycles so you wake during light sleep.
Why Sleep Cycles Matter
The 90-Minute Cycle
A complete sleep cycle lasts approximately 90 minutes and progresses through light sleep, deep sleep (slow-wave), and REM sleep. Waking during deep sleep causes sleep inertia — that groggy, disoriented feeling.
How Many Cycles?
Most adults need 5–6 full cycles (7.5–9 hours). Teenagers need 6–7 (9–10.5 hours). Older adults often naturally shift to 4–5 cycles. Quality matters more than quantity.
Improving Sleep Quality
Consistent sleep and wake times are more important than duration. Avoid screens 1 hour before bed, keep your room cool (16–18°C), and avoid caffeine after 2pm for significant sleep quality improvements.
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