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Waking between cycles is what feels different
Sleep runs through light stages, deep sleep and REM in a repeating loop of roughly 90 minutes. Waking near the end of a loop, in light sleep, feels ordinary; waking out of deep sleep in the middle of one produces the heavy, disoriented feeling that lasts a while. That is why six hours can feel better than seven, and it is what this calculator lines up.
Ninety minutes is an average, not your number
Cycle length varies between people and across a single night — commonly quoted as 80 to 110 minutes, and the later cycles carry more REM than the early ones. Treat the times below as a starting point rather than an alarm setting to defend. If waking consistently feels rough at one option, try the one on either side of it.
Falling asleep takes time, and it is counted here
A healthy adult typically takes about fifteen minutes to fall asleep, and this page builds that in: the bedtime shown is when to lie down, not when to be unconscious. Falling asleep in under five minutes regularly is a sign of not getting enough sleep, not of being good at sleeping.
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Frequently asked questions
QHow many cycles should I aim for?
Five or six for most adults, which is roughly seven and a half to nine hours. Four cycles, about six hours, works occasionally but not as a routine. Counting cycles is a way of landing on a whole number, not a licence to sleep less.
QIs the 90-minute figure exact?
No. It is an average; individual cycles commonly run from 80 to 110 minutes and lengthen through the night. If a suggested time consistently leaves you groggy, the option twenty minutes on either side is usually a better fit for you.
QWhy add fifteen minutes to fall asleep?
Because lying down and being asleep are not the same moment. Around fifteen minutes is typical for a healthy adult. If you routinely fall asleep in under five, that usually points to accumulated sleep debt rather than good sleep habits.
QDoes a nap follow the same rule?
Only partly. A short nap of twenty minutes stays in light sleep and avoids the heavy feeling entirely; a full 90-minute cycle also works. The times in between are the ones to avoid, because they land the alarm in deep sleep.