Question 1

What time should I wake up if I go to sleep at 11pm?

Accepted Answer

If you fall asleep at 11:00 PM (allowing 15 minutes to fall asleep, so sleep starts at 11:15 PM), the best wake-up times based on 90-minute sleep cycles are: 12:45 AM (1 cycle), 2:15 AM (2 cycles), 3:45 AM (3 cycles), 5:15 AM (4 cycles), 6:45 AM (5 cycles), or 8:15 AM (6 cycles — the ideal 9 hours). Most adults need 5–6 complete cycles (7.5–9 hours).

Question 2

How long is a sleep cycle?

Accepted Answer

A complete sleep cycle lasts approximately 90 minutes and consists of four stages: N1 (light sleep), N2 (deeper sleep), N3 (deep slow-wave sleep), and REM (rapid eye movement — when dreaming occurs). Most adults complete 4–6 cycles per night. Waking up at the end of a cycle rather than mid-cycle is why timing your alarm matters.

Question 3

Why do I wake up tired even after 8 hours of sleep?

Accepted Answer

You likely woke up mid-cycle — during deep sleep (N3) — rather than at the natural end of a 90-minute cycle. This causes 'sleep inertia,' the groggy, disoriented feeling that can last 30–60 minutes. Timing your alarm to coincide with the end of a sleep cycle (a multiple of 90 minutes after falling asleep) allows your body to wake naturally during the lighter N1 or N2 stage.

Question 4

How many hours of sleep do I need?

Accepted Answer

Most adults need 7–9 hours of sleep per night, which corresponds to 5–6 complete 90-minute sleep cycles. Teenagers need 8–10 hours (5–6+ cycles). Older adults often need slightly less, around 7–8 hours. Individual needs vary — the best indicator is whether you wake up feeling rested without an alarm.

Question 5

What time should I go to bed to wake up at 6am?

Accepted Answer

To wake up at 6:00 AM feeling refreshed, count back in 90-minute cycles, adding 15 minutes to fall asleep: 8:15 PM (6 cycles = 9 hrs), 9:45 PM (5 cycles = 7.5 hrs), 11:15 PM (4 cycles = 6 hrs), 12:45 AM (3 cycles = 4.5 hrs). The 9:45 PM or 8:15 PM bedtimes give you the optimal 7.5–9 hours of complete sleep cycles.

Question 6

What is REM sleep and why does it matter?

Accepted Answer

REM (Rapid Eye Movement) sleep is the final stage of each sleep cycle, lasting 20–25 minutes. During REM your brain consolidates memories, processes emotions, and restores cognitive function. Most dreaming occurs during REM sleep. Each successive cycle has longer REM periods, which is why cutting sleep short — even by 90 minutes — disproportionately reduces REM sleep and impairs memory and mood the next day.

Wake up
refreshed,
not groggy

Why sleep cycles matter

Common questions

Wake uprefreshed,not groggy

Why sleep cycles matter

Common questions

Wake up
refreshed,
not groggy