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Sleep Calculator
😴 Sleep Calculator
Waking up mid-cycle is what makes mornings feel groggy, not necessarily total sleep duration. This works backward from your wake-up time in 90-minute cycles to suggest bedtimes that align with natural sleep cycle boundaries.
A full sleep cycle (light sleep → deep sleep → REM) lasts roughly 90 minutes. Waking up at the end of a complete cycle, rather than in the middle of one, is widely reported to feel more refreshing even at the same total sleep duration — this tool offers several bedtime options, each ending on a clean cycle boundary.
Frequently Asked Questions
Is the 90-minute cycle length exact for everyone?
No — it's an average; individual cycle length varies by roughly 70-120 minutes person to person and even night to night, so treat the suggested bedtimes as a useful guide, not an exact science.
How much sleep do adults actually need?
Most health bodies recommend 7-9 hours for adults, which is why the calculator offers multiple cycle-count options (5 cycles ≈ 7.5 hours) rather than a single fixed number.
Does falling asleep instantly matter for this calculation?
The suggested bedtimes assume roughly 15 minutes to fall asleep, which is factored into the calculation — if you typically take longer, shift your bedtime earlier accordingly.
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